I want to develop method that will return the length of largest substring composed of identical characters form string that is passed as argument, but without using any of .NET libraries.
For example if we pass aaacccccdefffgg as parameter the biggest substring is ccccc and method should return 5.
Here is my working solution :
public static int GetMaxSubstringLenght(char[] myArray)
{
int max = 0;
for (int i = 0; i < myArray.Length-1; i++)
{
if (myArray.Length == 0)
{
return 0;
}
else
{
int j = i + 1;
int currentMax = 1; // string has some value, so we start with 1
while (myArray[i] == myArray[j])
{
currentMax++;
if (max < currentMax)
{
max = currentMax;
}
j++;
}
}
}
return max;
}
The code above will return expected result, but there will be some unnecessary iteration in for loop that I want to avoid. In first iteration when i=0it will compare it until j=2 and then will get out of while loop and start second iteration in for loop comparing the one at [1] index with [2], which we already did in previous iteration.So basically, when first iteration is completed, next one should start from the last value of j. How can I achieve that ?
Thank You in advance.
Since you want "Largest substring..." let's take String as argument and return String
public static String GetMaxSubstring(String value) {
if (String.IsNullOrEmpty(value))
return "";
int bestCount = 0;
char bestChar = '\0';
int currentCount = 0;
char current = '\0';
for (int i = 0; i < value.Length; ++i) {
if ((i == 0) || (value[i] != current))
currentCount = 0;
currentCount += 1;
current = value[i];
if (currentCount > bestCount) {
bestCount = currentCount;
bestChar = current;
}
}
return new String(bestChar, bestCount);
}
....
// "ccccc"
String result = GetMaxSubstring("aaacccccdefffgg");
// 5
int length = result.Length;
Another approach:
public static int MaxSubstringLength(string s)
{
if (string.IsNullOrEmpty(s))
return 0;
int max = 0, cur = 1;
for (int i = 1; i < s.Length; ++i, ++cur)
{
if (s[i] != s[i-1])
{
max = cur > max ? cur : max;
cur = 0;
}
}
return cur > max ? cur : max;
}
[EDIT] Simplified the code.
[EDIT2] Simplified the code further.
you also can do it with one loop:
public static int GetMaxSubstringLenght(char[] myArray)
{
int max = 0;
char currentchar = myArray[0];
int count = 1;
for each(char c in myArray)
{
if(currentchar != c)
{
count = 1;
currentchar = c;
}
if(count > max)
{
max = count;
}
count++;
}
return max;
}
I changed the code... now this code does not use math.max and I think I eleminated the mistake... I've no IDE at the moment to test it
public static int GetMaxSubstringLenght(char[] myArray)
{
if (myArray.Length == 0)
return 0;
if (myArray.Length == 1)
return 1;
int max = 1;
int localMax = 1;
for (int i = 0; i < myArray.Length - max; i++ )
{
if (myArray[i] == myArray[i + 1])
{
localMax++;
}
else
{
max = Math.Max(max, localMax);
localMax = 1;
}
}
return Math.Max(max, localMax);
}
static int LongestCharSequence(string s)
{
if (string.IsNullOrEmpty(s)) return 0;
var prevChar = '\0';
int cmax = 0;
int max = 1;
foreach (char c in s)
{
if (c != prevChar)
{
cmax = 1;
prevChar = c;
}
else
{
if (++cmax > max) max = cmax;
}
}
return max;
}
recursion!
static int LongestCharSequence(string s)
{
int i = (s?.Length ?? 0) == 0 ? 0 : 1;
for (; i < s?.Length; i++)
if (s[i] != s[i - 1]) return Math.Max(i, LongestCharSequence(s.Substring(i)));
return i;
}
Another solution using my favorite nested loop technique:
public static int MaxSubstringLength(string s)
{
int maxLength = 0;
for (int length = s != null ? s.Length : 0, pos = 0; pos < length;)
{
int start = pos;
while (++pos < length && s[pos] == s[start]) { }
maxLength = Math.Max(maxLength, pos - start);
}
return maxLength;
}
Related
I have a program that compares two integer value's length with this extension method
public static int NumDigits(this int n)
{
if (n < 0)
{
n = (n == int.MinValue) ? int.MaxValue : -n;
}
if (n < 10) return 1;
if (n < 100) return 2;
if (n < 1000) return 3;
if (n < 10000) return 4;
if (n < 100000) return 5;
if (n < 1000000) return 6;
if (n < 10000000) return 7;
if (n < 100000000) return 8;
return n < 1000000000 ? 9 : 10;
}
And it works perfectly. When I print the value of num1.numDigits(), the value returns 4 (it is worth '1111'. And my other integer: num2.numDigits() returns 2 (it is 11). This is great but when I actually compare them:
int[] rawNum2 = Arrays.DigitArr(num2);
if (num1.NumDigits() > num2.NumDigits())
{
int diff = num1.NumDigits() - num2.NumDigits();
for (int i = 1; i < diff; i++)
{
rawNum2.Append(0);
}
reversedNum2 = rawNum2.Reverse();
}
reversedNum2 is still '11' when it should be '0011'.
This is the class I compiled and used.
public static int[] Append(this int[] source, int value)
{
int[] newValue = source;
newValue = newValue.Concat(new[] { value }).ToArray();
return newValue;
}
public static int[] Reverse(this int[] array)
{
int[] arr = array;
for (int i = 0; i < arr.Length / 2; i++)
{
int tmp = arr[i];
arr[i] = arr[arr.Length - i - 1];
arr[arr.Length - i - 1] = tmp;
}
return arr;
}
public static int[] DigitArr(int n)
{
if (n == 0) return new int[1] { 0 };
var digits = new List<int>();
for (; n != 0; n /= 10)
digits.Add(n % 10);
var arr = digits.ToArray();
Array.Reverse(arr);
return arr;
}
Why is this happening?
You are discarding the return value of the Append method.
Change
rawNum2.Append(0);
to
rawNum2 = rawNum2.Append(0);
inside the for loop.
Your loop could be and should be simplified to:
rawNum2 = rawNum2.PadRight(num1.NumDigits(), '0')
To get the reversedNum2 as 0011 change your loop as below.
for (int i = 1; i <= diff; i++)
{
rawNum2=rawNum2.Append(0);
}
I made two changes changed the for loop to use i<=diff instead of i < diff
and assigning the return value from Append() method into the rawNum2.
I have to find subtext in text without using builtin function of string.
public static void Main(string[] args)
{
string subtext = "polly";
string text = "polly put the katle on,polly put the katle on,polly put the katle on,we all have tea";
int i, j, found;
int strLen, wordLen;
strLen = text.Length;
wordLen = subtext.Length;
for (i = 0; i < strLen - wordLen; i++)
{
found = 1;
for (j = 0; j < wordLen; j++)
{
if (text[i + j] != subtext[j])
{
found = 0;
break;
}
}
if (found == 1)
{
Console.WriteLine(" found at index:", subtext, i);
Console.ReadLine();
}
}
}
I am not sure how long you would like to search, your current code seems to find all indexes (or at least that seems to be the intent)
Some things you could change however is instead of always starting the loop, you could validate the if the char at position i matches the first char of the subtext, and if not continue.
When you want to write the data to the console, don't forget to add the spaceholders for your arguments, like:
Console.WriteLine("found {0} at index: {1}", subtext, i);
For the rest, I guess your current implementation is okay, but you could add some validations, like ensuring that both texts are available, and if subtext is longer than the text, simply return -1 directly.
For a simple find of first index, I wrote this one up, it still looks pretty similar to yours
private static int FindIn( string text, string sub ) {
if (string.IsNullOrWhiteSpace( text ) || string.IsNullOrWhiteSpace( sub ) ) {
return string.IsNullOrWhiteSpace( sub ) ? 0 : -1;
}
if (text.Length < sub.Length) {
return -1;
}
for (int i = 0; i < text.Length - sub.Length; i++) {
if (text[i] != sub[0]) {
continue;
}
var matched = true;
for (int j = 1; j < sub.Length && i + j < text.Length; j++) {
if (text[i+j] != sub[j]) {
matched = false;
break;
}
}
if (matched) {
return i;
}
}
return -1;
}
Which you can play around with here
There are a lot of pattern-matching algorithms in this book, i will leave here c# implementation of Knuth-Morris-Pratt algorithm.
static int[] GetPrefix(string s)
{
int[] result = new int[s.Length];
result[0] = 0;
int index = 0;
for (int i = 1; i < s.Length; i++)
{
while (index >= 0 && s[index] != s[i]) { index--; }
index++;
result[i] = index;
}
return result;
}
static int FindSubstring(string pattern, string text)
{
int res = -1;
int[] pf = GetPrefix(pattern);
int index = 0;
for (int i = 0; i < text.Length; i++)
{
while (index > 0 && pattern[index] != text[i]) { index = pf[index - 1]; }
if (pattern[index] == text[i]) index++;
if (index == pattern.Length)
{
return res = i - index + 1;
}
}
return res;
}
If you are looking for all occurance of the subtect in the text you can use the following code:
public static void Main(string[] args)
{
string subtext = "polly";
string text = "polly put the katle on,polly put the katle on,polly put the katle on,we all have tea";
int index = 0;
int startPosition = 0;
bool found = false;
while (index < text.Length - 1)
{
if (subtext[0] == text[index])
{
startPosition = index;
index++;
for (int j = 1; j <= subtext.Length - 1; j++)
{
if (subtext[j] != text[index])
{
found = false;
break;
}
else
{
found = true;
}
index++;
}
}
if (found)
{
Console.WriteLine("{0} found at index: {1}", subtext, startPosition);
found = false;
}
index++;
}
Console.ReadLine();
}
If you are looking only for the first occurance add break in the "if (found)" condition
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
i have written a small program to print out the sum of the 1000 first primes, but for some reason i get the wrong result.
namespace ConsoleApplication4
{
class Program
{
static void Main(string[] args)
{
long sum;
sum = 0;
int count;
count = 0;
for (long i = 0; count <= 1000; i++)
{
bool isPrime = true;
for (long j = 2; j < i; j++)
{
if (i != j && i % j == 0)
{
isPrime = false;
break;
}
}
if (isPrime)
{
sum += i;
count++;
}
}
Console.WriteLine(string.Format("{0}",sum));
Console.ReadLine();
}
}
}
result = 3674995 expected = 3682913
The implementation is identifying 1 as a prime, which is not correct; this can be fixed by initializing isPrime as follows.
bool isPrime = i != 1;
This yields the desired result 3682913; however the summand of 0 is also taken into account.
An efficient implementation checks for just prime divisors up to square root of the value; please, notice that all even values are not primes (with only exception - 2):
int count = 1000;
List<long> primes = new List<long>(count) {
2 }; // <- the only even prime
for (long value = 3; primes.Count < count; value += 2) {
long n = (long) (Math.Sqrt(value) + 0.1);
foreach (var divisor in primes)
if (divisor > n) {
primes.Add(value);
break;
}
else if (value % divisor == 0)
break;
}
// 3682913
Console.WriteLine(string.Format("{0}", primes.Sum()));
Console.ReadLine();
Try count = 1000000 and you'll get 7472966967499
long sum;
sum = 0;
int count;
count = 0;
for (long i = 0; count <= 1000; i++)
{
if (i == 1) continue;
bool isPrime = true;
for (long j = 2; j < i; j++)
{
if (i != j && i % j == 0)
{
isPrime = false;
break;
}
}
if (isPrime)
{
sum += i;
count++;
}
}
Console.WriteLine(string.Format("{0}", sum));
Console.ReadLine();
I recently had this question in an interview and this is what I came up with. Any feedback?
Find out how long the longest sequence is in a string. For example, in the string "abccdeeeeef" the answer would be 5.
static int LongestSeq(string strPass)
{
int longestSeq = 0;
char[] strChars = strPass.ToCharArray();
int numCurrSeq = 1;
for (int i = 0; i < strChars.Length - 1; i++)
{
if (strChars[i] == strChars[i + 1])
{
numCurrSeq++;
}
else
{
numCurrSeq = 1;
}
if (longestSeq < numCurrSeq)
{
longestSeq = numCurrSeq;
}
}
return longestSeq;
}
This will return 0 for strings of length 1 (when it should return 1).
First comment: you don't need to convert it to a char array. You can index straight into the string.
Second comment: you could easily generalize this to IEnumerable<T> if you wanted to, using foreach and remembering the "current" item.
Third comment: I think the comparison between longestSeq and numCurrSeq would be clearer as:
if (numCurrSeq > longestSeq)
To me that's more natural as I usually have the varying part of the expression first.
Just to add my 2 pence in, here's an alternative using Regex:
string source = "eeabccdeeeeef";
Regex reg = new Regex(#"(\w)\1+");
MatchCollection matches = reg.Matches(source);
int longest = 0;
foreach (System.Text.RegularExpressions.Match match in matches)
{
if (longest < match.Length) longest = match.Length;
}
Due to not reading the question properly in the first place when posting my previous answer, I should probably add in some actual feedback considering that's the question posted by the OP. However, every point I've come up with has been mentioned by Henrik or Job Skeet, so I'll just stress the point Jon Skeet made; you do not have to convert a string to a char array, you can just index a particular point in the string as follows:
char letter = someString[4];
So it should all still work if you replace strChars with strPass.
You can always rember the last character, so you don't need to access the array twice in an iteration.
Inside your loop you can use another loop which iterates as long as the current character is the same as the last character. After this subloop you can place the check if the current numCurrSeq > longestSeq you you don't need this check every iteration but for every subsequence.
I don't really know whatever langauge this is (C#?) so excuse any minor syntactic glitches (I don't know if it's "else if" or "elseif" or "elif" or something else)
static int LongestSeq(string strPass)
{
int longestSeq = 1;
int curSeqStart = 0;
for (int i = 1; i < strPass.Length; i++)
{
if (strPass[i] != strPass[curSeq])
{
curSeqStart = i;
}
else if (i - curSeqStart + 1 > longestSeq)
{
longestSeq = i - curSeqStart + 1;
}
}
return longestSeq;
}
It might be more efficient to do
...
else
{
len = i - curSeqStart + 1
if ( len > longestSeq )
{
longestSeq = len;
}
}
or even just
...
else
{
longestSeq = max(longestSeq, i - curSeqStart + 1)
}
depending on how good your 'max' implementation and compiler are.
I think this works? I don't ussually write recursive methods, I would have totally come up with the posters answer..
public static int recurse(Char last, int seqLength, int currentIndex, int largestSeqLength, string source)
{
if (currentIndex > source.Length)
{
return largestSeqLength;
}
if (source[currentIndex] == last)
{
seqLength++;
if (seqLength > largestSeqLength)
{
largestSeqLength = seqLength;
}
}
else
{
seqLength = 1;
}
return recurse(source[currentIndex], seqLength, currentIndex++, largestSeqLength, source);
}
And another implementation
public static int LongestSeq<T>(this IEnumerable<T> source)
{
if (source == null)
throw new ArgumentNullException("source");
int result = 0;
int currentCount = 0;
using (var e = source.GetEnumerator())
{
var lhs = default(T);
if (e.MoveNext())
{
lhs = e.Current;
currentCount = 1;
result = currentCount;
}
while (e.MoveNext())
{
if (lhs.Equals(e.Current))
{
currentCount++;
}
else
{
currentCount = 1;
}
result = Math.Max(currentCount, result);
lhs = e.Current;
}
}
return result;
}
A simple (untested) solution would be:
int GetLongestSequence(string input)
{
char c = 0;
int maxSequenceLength = 0;
int maxSequenceStart = 0;
int curSequenceLength = 0;
int length = input.Length;
for (int i = 0; i < length; ++i)
{
if (input[i] == c)
{
++curSequenceLength;
if (curSequenceLength > maxSequenceLength)
{
maxSequenceLength = curSequenceLength;
maxSequenceStart = i - (curSequenceLength - 1);
}
}
else
{
curSequenceLength = 1;
c = input[i];
}
}
return maxSequenceStart;
}
Or a better structured code (also untested):
private int GetSequenceLength(string input, int start)
{
int i = start;
char c = input[i];
while (input[i] == c) ++i; // Could be written as `while (input[i++] == c);` but i don't recommend that
return (i - start);
}
public int GetLongestSequence(string input)
{
int length = input.Length;
int maxSequenceLength = 0;
int maxSequenceStart = 0;
for (int i = 0; i < length; /* no ++i */)
{
int curSequenceLength = this.GetSequenceLength(input, i);
if (curSequenceLength > maxSequenceLength)
{
maxSequenceLength = curSequenceLength;
maxSequenceStart = i;
}
i += curSequenceLength;
}
return maxSequenceStart;
}
This extension method find the longest sequence of same characters in a string.
public static int GetLongestSequenceOfSameCharacters(this string sequence)
{
var data = new List<char>();
for (int i = 0; i < sequence.Length; i++)
{
if (i > 0 && (sequence[i] == sequence[i - 1]))
{
data.Add(sequence[i]);
}
}
return data.GroupBy(x => x).Max(x => x.Count()) + 1;
}
[TestMethod]
public void TestMethod1()
{
// Arrange
string sequence = "aabbbbccccce";
// Act
int containsSameNumbers = sequence.GetLongestSequenceOfSameCharacters();
// Assert
Assert.IsTrue(containsSameNumbers == 5);
}