I am using this backtracking soduku solving algorithm which is really good and efficient
private void solve()
{
for (var y = 8; y >= 0; y--)
{
for (var x = 8; x >= 0; x--)
{
var a = grid[y, x];
if (a == 0)
{
for (var n = 1; n <= 9; n++)
{
if (possible(y, x, n))
{
grid[y, x] = n;
solve();
grid[y, x] = 0;
}
}
return;
}
}
}
print();
}
The thing is i want to add a little change which I haven't been able to do and it is that instead of trying numbers 1 to 9 in order i want it to choose a random number from 1 to 9, and then set it in the grid, without repetition of course.
public static class MyRandomGenerator
{
private static Random random = new Random();
public static int[] Generate(int inclusiveMinValue, int exclusiveMaxValue)
{
if (exclusiveMaxValue <= inclusiveMinValue)
throw new ArgumentException(nameof(exclusiveMaxValue));
var capacity = exclusiveMaxValue - inclusiveMinValue;
var result = new HashSet<int>(capacity);
while (result.Count < capacity)
{
result.Add(random.Next(inclusiveMinValue, exclusiveMaxValue));
}
return result.ToArray();
}
}
Related
I am a total newbie to programming and i have been following some tutorials on array related to housie ticket generator.The point where I am stuck is that, I have to check each rows and each rows of the 3x9 matrix should not have more the two empty cells or it cannot have more then two cells filled next to each other.I am putting random numbers on the arrays and trying to validate the rules but,the program crashes. Can someone please give me an idea.?
This is what i've tried.
for(int columnIndex=0;columnIndex<=6;columnIndex++)
{
if(game[i,columnIndex+2]!=0)
{
return -1;
}
}
And this is the whole code
using System;
namespace HelloWorld
{
class Program
{
public static void Main (String[] args)
{
for(int times=0;times<2;times++)
{
startGame();
Console.WriteLine("******************************************************************");
}
}
private static void startGame()
{
int[,] game = new int[3, 9];
int occupancyLimit = 15;
while (occupancyLimit > 0)
{
int i = getRandomNumber(3);
int j = getRandomNumber(9);
//Console.Write(i);
//Console.Write(j);
// Console.Write(game[i,j]+" ");
int data = validateAndReturnNumber(i, j, game);
if (data>0)
{
game[i, j] = data;
occupancyLimit--;
//Console.WriteLine(game[i,j]);
}
}
for (int i = 0; i < game.GetLength(0); i++)
{
for (int j = 0; j < game.GetLength(1); j++)
{
Console.Write(game[i,j] + "\t");
}
Console.WriteLine();
}
}
private static int validateAndReturnNumber(int i, int j, int[,] game)
{
//do not override existing elements in array
if (game[i,j] != 0)
{
return -1;
}
//column cannot have more then two elements
int columncounter = 0;
for(int c=0;c<3;c++)
{
if(game[c,j]!=0)
{
columncounter++;
}
}
if(columncounter>=2)
{
return -1;
}
/*
//rows cannot have more then two cells filled in and
//rows cannot have more then two empty cells
for(int columnIndex=0;columnIndex<=6;columnIndex++)
{
if(game[i,columnIndex+2]!=0)
{
return -1;
}
}
*/
// rows cannot have more then 5 elements
int rowcounter = 0;
for(int r=0;r<9;r++)
{
if(game[i,r]!=0)
{
rowcounter++;
}
}
//Applying, rows cannot have more then 5 elements
if(rowcounter>=5)
{
return -1;
}
//return getRandomNumberForColumn(j);
int data = 0;
Boolean isValueSet = false;
do
{
data = getRandomNumberForColumn(j);
isValueSet = isValueExistsInCol(game, i, j, data);
} while (isValueSet);
return data;
}
private static bool isValueExistsInCol(int[,] game, int i, int j, int data)
{
Boolean status = false;
for(int k=0;k<3;k++)
{
if(game[k,j]==data)
{
status = true;
break;
}
}
return status;
}
private static int getRandomNumberForColumn(int high)
{
if(high==0)
{
high = 10;
}
else
{
high=(high + 1) * 10;
}
int low = high - 9;
Random random = new Random();
return random.Next(high-low)+low;
}
private static int getRandomNumber(int max)
{
Random random = new Random();
int num=random.Next(max);
return (num);
}
}
}
Why your for loop does not work:
for (int columnIndex = 0; columnIndex <= 6; columnIndex++)
{
if (game[i, columnIndex + 2] != 0)
{
return -1;
}
}
This loop does not take j into account. It is testing for previous numbers added, as soon as one previous number fails this test, it will fail indefinitely. This creates an infinite loop. This loop also fails if a number is placed in any position past 1, while it needs to fill 5 positions to succeed. This is mathematically impossible.
This:
'should not have more the two empty cells or it cannot have more then two cells' is also mathematically impossible. a row of 9 cannot have less than 2 full and less than 2 empty at the same time.
I think you are after 2 empty or full consecutively in a row. For that testing for two empty in a row cannot be achieved as it starts empty, and you are testing it before you fill it. Fortunately this is a redundant test that will always be true based on all of the other test cases.
No more than 2 full in a row is possible, but can also lead to impossible scenarios. I have added a check that resets the scenario if it has not found the solution after 1000 guesses.
using System;
namespace HelloWorld
{
class Program
{
public static void Main(String[] args)
{
for (int times = 0; times < 2; times++)
{
startGame();
// Console.WriteLine("******************************************************************");
}
}
private static void startGame()
{
int iCount = 0;
int[,] game = new int[3, 9];
int occupancyLimit = 15;
while (occupancyLimit > 0)
{
int i = getRandomNumber(3);
int j = getRandomNumber(9);
//Console.Write(i);
//Console.Write(j);
// Console.Write(game[i,j]+" ");
int data = validateAndReturnNumber(i, j, game);
if (data > 0)
{
game[i, j] = data;
occupancyLimit--;
//Console.WriteLine(game[i,j]);
}
else
{
iCount++;
//Console.WriteLine(iCount);
//printGame(game);
// If X many fails, retry
if(iCount > 1000)
{
iCount = 0;
game = new int[3, 9];
occupancyLimit = 15;
}
}
// If you want to check for zeros you would need to do it here. And use while(true) above
/*
if( //Check for zeros)
{
break; // Ends While loop
}
else
{
// Reset and try again
iCount = 0;
game = new int[3, 9];
occupancyLimit = 15;
}
*/
}
printGame(game);
}
private static void printGame(int[,] game)
{
for (int i = 0; i < game.GetLength(0); i++)
{
for (int j = 0; j < game.GetLength(1); j++)
{
Console.Write(game[i, j] + "\t");
}
Console.WriteLine();
}
Console.WriteLine("******************************************************************");
}
private static int validateAndReturnNumber(int i, int j, int[,] game)
{
//do not override existing elements in array
if (game[i, j] != 0)
{
return -1;
}
//column cannot have more then two elements
int columncounter = 0;
for (int c = 0; c < 3; c++)
{
if (game[c, j] != 0)
{
columncounter++;
}
}
if (columncounter >= 2)
{
return -1;
}
if(
(j != 0 && j != 1 && game[i, j - 2] != 0 && game[i, j - 1] != 0) || // 12X
(j != 0 && j != 8 && game[i, j - 1] != 0 && game[i, j + 1] != 0) || // 1X3
(j != 7 && j != 8 && game[i, j + 1] != 0 && game[i, j + 2] != 0) // X23
)
{
return -1;
}
//for (int columnIndex = 0; columnIndex <= 6; columnIndex++)
//{
// if (game[i, columnIndex + 2] != 0)
// {
// return -1;
// }
//}
// rows cannot have more then 5 elements
int rowcounter = 0;
for (int r = 0; r < 9; r++)
{
if (game[i, r] != 0)
{
rowcounter++;
}
}
//Applying, rows cannot have more then 5 elements
if (rowcounter >= 5)
{
return -1;
}
//return getRandomNumberForColumn(j);
int data = 0;
Boolean isValueSet = false;
do
{
data = getRandomNumberForColumn(j);
isValueSet = isValueExistsInCol(game, i, j, data);
} while (isValueSet);
return data;
}
private static bool isValueExistsInCol(int[,] game, int i, int j, int data)
{
Boolean status = false;
for (int k = 0; k < 3; k++)
{
if (game[k, j] == data)
{
status = true;
break;
}
}
return status;
}
private static int getRandomNumberForColumn(int high)
{
if (high == 0)
{
high = 10;
}
else
{
high = (high + 1) * 10;
}
int low = high - 9;
Random random = new Random();
return random.Next(high - low) + low;
}
private static int getRandomNumber(int max)
{
Random random = new Random();
int num = random.Next(max);
return (num);
}
}
}
Cheers!
I have an array of n integers and I need to divide any of it's elements by 2 (return the ceiling of the result) for k times such that the sum is minimum. The value of k can be very large as compared to n.
I am using this code:
private static int GetMaxSum(int[] array, int k)
{
int n = array.Length;
for (int i = 0; i < k; i++)
{
var indexAtMax = GetMaxIndex(array);
if (array[indexAtMax] == 1) break;
array[indexAtMax] = array[indexAtMax] / 2 + array[indexAtMax] % 2;
}
return array.Sum();
}
private static int GetMaxIndex(int[] array)
{
int maxIndex = 0;
int max = array[0];
for (int i=1; i<array.Length;i++)
{
if (array[i] > max)
{
max = array[i];
maxIndex = i;
}
}
return maxIndex;
}
How can we improve the performance further probably by using max heap or some other data structure?
Unless I'm misunderstanding your requirements, your solution seens way too complicated (and apparently wrong according to comments).
I can't really think this through right now, but wouldn't it be the case that the global solution is made up of optimal intermediate steps? The order in which you divide is irrelevant and the problem is linear.
If that is the case, you simply have to evaluate the optimal division in each step and that is not very hard to do:
static void Minimize(int[] arr, int k)
{
for (var j = 0; j < k; j++)
{
var maxGainIndex = -1;
var maxGain = int.MinValue;
for (var i = 0; i < arr.Length; i++)
{
var gain = arr[i] - (arr[i]/2 + arr[i] % 2);
if (gain > maxGain)
{
maxGain = gain;
maxGainIndex = i;
}
}
arr[maxGainIndex] -= maxGain;
}
}
If I'm not wrong, the asymptotic behavior of this algorithm is O(k·n).
UPDATE:
Based on claims of posted code being far less optimal, I've taken the liberty of benchmarking both algorithms with these results on my machine:
Input array: 100;120;80;55;75;115;125;150;90;35;65;77;89;10;11;113;200;300
Number of divisions: 20
Running benchmarks in Release mode without debugger attached.
1000000 of GetMimimum finished in 584 ms with result 704.
1000000 of GetMimimum2 finished in 8846 ms with result 704.
Benchmarking code can be found here: https://dotnetfiddle.net/ITx53q
The performance gain of my proposed algorithm is rather staggering (x15), which was expected because your solution is, as evaluated initally, overcomplicated at best for such a simple problem.
As the assumption was that k>>n, the simpler algorithms are of the order O(kn) which can be too much of iterations.
I have written this code thinking of the problem and how can I limit sorting or calculating min/max. I have divided the array into subarrays so that the operations can be performed on subarrays without thinking of the order of operations.
private static int GetMinSum(int[] array, int k)
{
int n = array.Length;
var sum = 0;
k = GetOptimizedListAndK(array, n, k, out var lists);
//If more sublists are needed
if (k > 0)
{
var count = lists.CountSum;
var key = lists.Key;
if (key > 0)
{
var poweroftwo = 1 << key;
sum += count * poweroftwo - k * poweroftwo / 2;
var dictionary2 = GetDictionary(array, lists, poweroftwo);
key = dictionary2.Keys.Last();
while (k > 0 && key > 0)
{
var list2 = dictionary2[key];
count = list2.Count;
if (k >= count)
{
list2.ForEach(
index => array[index] = array[index] / 2 + array[index] % 2);
dictionary2.Remove(key);
key = dictionary2.Keys.LastOrDefault();
k -= count;
}
else
{
if (k <= Log2(count))
{
for (int i = 0; i < k; i++)
{
var indexAtMax = GetMaxIndex(list2, array);
array[indexAtMax] = array[indexAtMax] / 2 + array[indexAtMax] % 2;
}
k = 0;
}
if (count - k <= Log2(count))
{
var minIndexes = GetMinIndexes(list2, array, count - k);
foreach (var i in list2)
{
if (!minIndexes.Contains(i))
{
array[i] = array[i] / 2 + array[i] % 2;
}
}
k = 0;
}
if (k > 0)
{
poweroftwo = 1 << key;
sum += list2.Count * poweroftwo - k * poweroftwo / 2;
dictionary2 = GetDictionary(array, list2, poweroftwo);
key = dictionary2.Keys.Last();
}
}
}
}
}
return array.Sum() + sum;
}
private static int GetOptimizedListAndK(int[] array, int n, int k, out Lists lists)
{
lists = null;
Dictionary<int, Lists> dictionary = new Dictionary<int, Lists>();
PopulatePowerBasedDictionary(array, n, dictionary);
var key = dictionary.Keys.Max();
while (key > 0 && k > 0)
{
lists = dictionary[key];
var count = lists.CountSum;
if (k >= count)
{
lists.ForEach(list => list.ForEach(index => array[index] = array[index] / 2 + array[index] % 2));
if (key > 1)
{
if (dictionary.TryGetValue(key - 1, out var lowerlists))
{
lowerlists.AddRange(lists);
lowerlists.CountSum += count;
}
else dictionary.Add((key - 1), lists);
}
dictionary.Remove(key);
key--;
k -= count;
}
else
{
if (k < Log2(count))
{
for (int i = 0; i < k; i++)
{
var indexAtMax = GetMaxIndex(lists, array);
array[indexAtMax] = array[indexAtMax] / 2 + array[indexAtMax] % 2;
}
k = 0;
}
if (count - k < Log2(count))
{
var minIndexes = GetMinIndexes(lists, array, count - k);
foreach (var list in lists)
{
foreach (var i in list)
{
if (!minIndexes.Contains(i))
{
array[i] = array[i] / 2 + array[i] % 2;
}
}
}
k = 0;
}
break;
}
}
return k;
}
private static void PopulatePowerBasedDictionary(int[] array, int n, Dictionary<int, Lists> dictionary)
{
for (int i = 0; i < n; i++)
{
if (array[i] < 2) continue;
var log2 = Log2(array[i]);
if (dictionary.TryGetValue(log2, out var lists))
{
lists[0].Add(i);
lists.CountSum++;
}
else
{
lists = new Lists(1,log2) { new List<int> { i } };
dictionary.Add(log2, lists);
}
}
}
private static int GetMaxIndex(List<int> list, int[] array)
{
var maxIndex = 0;
var max = 0;
foreach (var i in list)
{
if (array[i] > max)
{
maxIndex = i;
max = array[i];
}
}
return maxIndex;
}
private static SortedDictionary<int, List<int>> GetDictionary(int[] array, Lists lists, int poweroftwo)
{
SortedDictionary<int, List<int>> dictionary = new SortedDictionary<int, List<int>>();
foreach (var list in lists)
{
foreach (var i in list)
{
array[i] = array[i] - poweroftwo;
if (array[i] < 2)
{
continue;
}
var log2 = Log2(array[i]);
if (dictionary.TryGetValue(log2, out var list2))
{
list2.Add(i);
}
else
{
list2 = new List<int> { i };
dictionary.Add(log2, list2);
}
}
}
return dictionary;
}
private static SortedDictionary<int, List<int>> GetDictionary(int[] array, List<int> list, int poweroftwo)
{
SortedDictionary<int, List<int>> dictionary = new SortedDictionary<int, List<int>>();
foreach (var i in list)
{
array[i] = array[i] - poweroftwo;
if (array[i] < 2)
{
continue;
}
var log2 = Log2(array[i]);
if (dictionary.TryGetValue(log2, out var list2))
{
list2.Add(i);
}
else
{
list2 = new List<int> { i };
dictionary.Add(log2, list2);
}
}
return dictionary;
}
private static int GetMaxIndex(Lists lists, int[] array)
{
var maxIndex = 0;
var max = 0;
foreach (var list in lists)
{
foreach (var i in list)
{
if (array[i]>max)
{
maxIndex = i;
max = array[i];
}
}
}
return maxIndex;
}
private static HashSet<int> GetMinIndexes(Lists lists, int[] array, int k)
{
var mins = new HashSet<int>();
var minIndex = 0;
var min = int.MaxValue;
for (int j = 0; j < k; j++)
{
foreach (var list in lists)
{
foreach (var i in list)
{
if (array[i] < min && !mins.Contains(i))
{
minIndex = i;
min = array[i];
}
}
}
mins.Add(minIndex);
min = int.MaxValue;
}
return mins;
}
private static HashSet<int> GetMinIndexes(List<int> list, int[] array, int k)
{
var mins = new HashSet<int>();
var minIndex = 0;
var min = int.MaxValue;
for (int j = 0; j < k; j++)
{
foreach (var i in list)
{
if (array[i] < min && !mins.Contains(i))
{
minIndex = i;
min = array[i];
}
}
mins.Add(minIndex);
min = int.MaxValue;
}
return mins;
}
private static int Log2(int n)
{
return BitOperations.Log2((uint)n);
}
Lists Class:
public class Lists:List<List<int>>
{
public int Key { get; set; }
public int CountSum { get; set; }
public Lists(int countSum, int key):base()
{
CountSum = countSum;
Key = key;
}
}
I tried to improvise a random number generator by using the "Bays & Durham Randomization by Shuffling" algorithm. I followed a tutorial online and made this code:
public int[] GenerateRandomSequence_Improved(int n, int min, int max)
{
int[] seq = new int[n];
for(int i = 0; i < n; i++)
{
int rand = GenerateNextRandomNumber(min, max);
rand = min + rand % (max + 1 - min);
seq[i] = rand;
}
return seq;
}
I wanna know if I did it correctly or not..
EDIT: This is the code for the GenerateNextRandomNumber method
public int GenerateNextRandomNumber(int min, int max)
{
return cSharpRNG.Next(min,max);
}
According to Knuth TAOCP Vol. 2 p. 34 Algorithm B, the proper algorithm is the following,
public class BaysDurham
{
private readonly int[] t;
private int y; // auxiliary variable
// Knuth TAOCP Vol. 2 p. 34 Algorithm B
public BaysDurham(int k)
{
t = new int[k];
for (int i = 0; i < k; i++)
{
t[i] = rand.Next();
}
y = rand.Next();
}
public int Next()
{
var i = (int)((t.Length * (long) y) / int.MaxValue); // mitigates the bias
y = t[i];
t[i] = rand.Next();
return y;
}
private readonly Random rand = new Random();
}
I let you adapt the range of the output, but just know that the formula you use with the modulo introduce significant bias and makes the distribution non-uniform please look at this.
Here is what I believe proper implementation of the Bays-Durham shuffling. Warning wrt bias in indexing due to modulo operation is right though.
.NET Core 2.2, x64 Win10
using System;
using System.Diagnostics;
namespace BaysDurhamShuffling
{
public class BaysDurhamRNG
{
public int[] _table;
public int _xnext;
public Random _rng = null;
public BaysDurhamRNG(int n, int seed = 312357) {
Debug.Assert(n > 1);
_rng = new Random(seed);
_table = new int [n];
for(int k = 0; k != n; ++k) {
_table[k] = _rng.Next();
}
_xnext = _rng.Next();
}
public int next() {
var x = _xnext; // store return value
var j = _xnext % _table.Length; // form the index j into the table
_xnext = _table[j]; // get jth element of table and to copy it to the output stream on next call
_table[j] = _rng.Next(); // replace jth element of table with next random value from input stream
return x; // return what was stored in next value
}
}
class Program
{
static void Main(string[] args)
{
var rng = new BaysDurhamRNG (16, 12345);
for(int k = 0; k != 30; ++k) {
var x = rng.next();
Console.WriteLine($"RV = {x}");
}
}
}
}
Find the sum of all prime numbers not greater than N. For example if user input 5 then prime numbers are 2,3,5 and their sum is 10. It is not passing 4 test cases in which two of them are exceeding the time limit. I have tried several test cases and my code is working fine on them. Here is my code.
public static long sieve_of_eratosthenes(long n)
{
if (n == 1)
{
// If the user input 1.
return (0);
}
else
{
long sum = 0;
bool[] array = new bool[n + 1];
for (long i = 2; i <= n; i++)
{
// Setting all values to true.
array[i] = true;
}
// Eliminating the composite numbers.
for (long j = 2; j < Math.Sqrt(n); j++)
{
if (array[j])
{
long multiple = 1;
for (long k = (j * j); k <= n; k = (j * j) + (j * (multiple++)))
{
array[k] = false;
}
}
}
//Now we have the prime numbers. We just have to add them.
for (int z = 2; z <= n; z++)
{
if (array[z])
{
sum = sum + z;
}
}
return (sum);
}
}
static void Main(string[] args)
{
int noofcases = int.Parse(Console.ReadLine());
for( int i = 0; i < noofcases; i ++)
{
long entry = long.Parse(Console.ReadLine());
Console.WriteLine(sieve_of_eratosthenes(entry));
}
}
check the below code. I wrote simple logic which you can improve
public static class Int32Extension
{
public static bool IsPrime(this int number)
{
if (number <= 1) return false;
if (number == 2) return true;
if (number % 2 == 0) return false;
var boundary = (int)Math.Floor(Math.Sqrt(number));
for (int i = 3; i <= boundary; i += 2)
if (number % i == 0)
return false;
return true;
}
}
then
static void Main(string[] args)
{
int input = 5;
int sum = 0;
for (int i = 0; i < input;)
{
if (!(++i).IsPrime())
continue;
sum += i;
}
Console.WriteLine(sum);
}
Without using Extension Method
public static bool IsPrime(int number)
{
if (number <= 1) return false;
if (number == 2) return true;
if (number % 2 == 0) return false;
var boundary = (int)Math.Floor(Math.Sqrt(number));
for (int i = 3; i <= boundary; i += 2)
if (number % i == 0)
return false;
return true;
}
static void Main(string[] args)
{
int input = 5;
int sum = 0;
for (int i = 0; i < input;)
{
if (!IsPrime(++i))
continue;
sum += i;
}
Console.WriteLine(sum);
}
.Net Fiddle Link : https://dotnetfiddle.net/rEBY9r
Edit : The IsPrime test uses Primality Test With Pseudocode
Given an array A with zero index and N integers find equal elements with different positions in the array. Pair of indexes (P,Q) such that 0 <= P < Q < N such that A[P] = A[Q]. My algorithm is below but I am looking for a O(N*logN) solution.
public int solution(int[] A)
{
int N = A.Length;
int count = 0;
for (int j = 0; j < N; j++)
{
count += FindPairs(A[j], j, A);
}
return count;
}
public int FindPairs(int item, int ci, int[] A)
{
int len = A.Length;
int counter=0;
int k = ci+1;
while (k < len)
{
if (item == A[k])
counter++;
k++;
}
return counter;
}
From your code, it looks like the goal is to return the count of ascending duplicate pairs in A.
We observe that if there are m occurrences of the number x in A, then the number of ascending duplicate pairs of the value x is m choose 2, or m (m - 1) / 2.
So, we sum up m (m - 1) / 2 for each unique x, giving us the answer.
In pseudocode, this looks like:
count = new Dictionary();
foreach a in A {
count[a]++;
}
total = 0;
foreach key, value in count {
total += value * (value - 1) / 2;
}
return total;
This algorithm is O(N).
Recent interview question … here is what I did:
using System;
using System.Collections.Generic;
using System.Linq;
namespace Codility
{
internal class Program
{
public struct Indice
{
public Indice(int p, int q)
{
P = p;
Q = q;
}
public int P;
public int Q;
public override string ToString()
{
return string.Format("({0}, {1})", P, Q);
}
}
private static void Main(string[] args)
{
// 0 1 2 3 4 5
int[] list = new int[] {3,3,3,3,3,3};
int answer = GetPairCount(list);
Console.WriteLine("answer = " + answer);
Console.ReadLine();
}
private static int GetPairCount(int[] A)
{
if (A.Length < 2) return 0;
Dictionary<int, Dictionary<Indice, Indice>> tracker = new Dictionary<int, Dictionary<Indice, Indice>>();
for (int i = 0; i < A.Length; i++)
{
int val = A[i];
if (!tracker.ContainsKey(val))
{
Dictionary<Indice, Indice> list = new Dictionary<Indice, Indice>();
Indice seed = new Indice(i, -1);
list.Add(seed, seed);
tracker.Add(val, list);
}
else
{
Dictionary<Indice, Indice> list = tracker[val];
foreach (KeyValuePair<Indice,Indice> item in list.ToList())
{
Indice left = new Indice(item.Value.P, i);
Indice right = new Indice(i, item.Value.Q);
if (!list.ContainsKey(left))
{
list.Add(left, left);
Console.WriteLine("left= " + left);
}
if (!list.ContainsKey(right))
{
list.Add(right, right);
Console.WriteLine("\t\tright= " + right);
}
}
}
}
return tracker.SelectMany(kvp => kvp.Value).Count(num => num.Value.Q > num.Value.P);
}
}
}
I think this is best version I got in c#.
static void Main(string[] args)
{
var a = new int[6] { 3, 5, 6, 3, 3, 5 };
//Push the indices into an array:
int[] indices = new int[a.Count()];
for (int p = 0; p < a.Count(); ++p) indices[p] = p;
//Sort the indices according to the value of the corresponding element in a:
Array.Sort(indices, (k, l) =>Compare(a[k], a[l]));
//Then just pull out blocks of indices with equal corresponding elements from indices:
int count = 0;
int i = 0;
while (i < indices.Count())
{
int start = i;
while (i < indices.Count() && a[indices[i]] == a[indices[start]])
{
++i;
}
int thisCount = i - start;
int numPairs = thisCount * (thisCount - 1) / 2;
count += numPairs;
}
Console.WriteLine(count);
Console.ReadKey();
}
//Compare function to return interger
private static int Compare(int v1, int v2)
{
if (v2 > v1)
return 1;
if (v1 == v2)
return 0;
else
return -1;
}
This approach has O(n log n) complexity overall, because of the sorting. The counting of the groups is linear.
Try this:
private static int GetIdenticalPairCount(int[] input)
{
int identicalPairCount = 0;
Dictionary<int, int> identicalCountMap = new Dictionary<int, int>();
foreach (int i in input)
{
if (identicalCountMap.ContainsKey(i))
{
identicalCountMap[i] = identicalCountMap[i] + 1;
if (identicalCountMap[i] > 1)
{
identicalPairCount += identicalCountMap[i];
}
else
{
identicalPairCount++;
}
}
else
{
identicalCountMap.Add(i, 0);
}
}
return identicalPairCount;
}
Test my version:
public int solution(int[] A)
{
int N = A.Length;
int count = 0;
for (int j = 0; j < N - 1; j++)
for (int i = j + 1; i < N; i++)
if (A[i] == A[j])
count++;
return count;
}