# Length of longest substring having all characters as K

Given a string **S** and a character **K**. The task is to find the length of the longest substring of S having all characters the same as character K.

**Examples: **

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Input:S = “abcd1111aabc”, K = ‘1’Output:4Explanation:

1111 is the largest substring of length 4.

Input:S = “#1234#@@abcd”, K = ‘@’Output:2Explanation:

@@ is the largest substring of length 2.

**Approach: **The idea is to iterate over the string and check the following two conditions:

- If the current character is the
**same**as character K then increase the value of the counter by one. - If the current character is not the same as K then update the previous count and reinitialize the counter to 0.
- Repeat the steps above till the length of the string.

Below is the implementation of the above approach:

## C++

`// C++ program for the above approach` `#include <bits/stdc++.h>` `using` `namespace` `std;` `// Function to find the length of` `// longest sub-string having all` `// characters same as character K` `int` `length_substring(string S, ` `char` `K)` `{` ` ` `// Initialize variables` ` ` `int` `curr_cnt = 0, prev_cnt = 0, max_len;` ` ` `// Iterate till size of string` ` ` `for` `(` `int` `i = 0; i < S.size(); i++) {` ` ` `// Check if current character is K` ` ` `if` `(S[i] == K) {` ` ` `curr_cnt += 1;` ` ` `}` ` ` `else` `{` ` ` `prev_cnt = max(prev_cnt, curr_cnt);` ` ` `curr_cnt = 0;` ` ` `}` ` ` `}` ` ` `prev_cnt = max(prev_cnt, curr_cnt);` ` ` `// Assingning the max` ` ` `// value to max_len` ` ` `max_len = prev_cnt;` ` ` `return` `max_len;` `}` `// Driver code` `int` `main()` `{` ` ` `string S = ` `"abcd1111aabc"` `;` ` ` `char` `K = ` `'1'` `;` ` ` `// Function call` ` ` `cout << length_substring(S, K);` ` ` `return` `0;` `}` |

## Java

`// Java program for` `// the above approach` `import` `java.util.*;` `class` `GFG {` `// Function to find the length of` `// longest sub-string having all` `// characters same as character K` `static` `int` `length_substring(String S,` ` ` `char` `K)` `{` ` ` `// Initialize variables` ` ` `int` `curr_cnt = ` `0` `, prev_cnt = ` `0` `,` ` ` `max_len;` ` ` `// Iterate till size of string` ` ` `for` `(` `int` `i = ` `0` `; i < S.length(); i++)` ` ` `{` ` ` `// Check if current character is K` ` ` `if` `(S.charAt(i) == K)` ` ` `{` ` ` `curr_cnt += ` `1` `;` ` ` `}` ` ` `else` ` ` `{` ` ` `prev_cnt = Math.max(prev_cnt,` ` ` `curr_cnt);` ` ` `curr_cnt = ` `0` `;` ` ` `}` ` ` `}` ` ` `prev_cnt = Math.max(prev_cnt,` ` ` `curr_cnt);` ` ` `// Assingning the max` ` ` `// value to max_len` ` ` `max_len = prev_cnt;` ` ` `return` `max_len;` `}` `// Driver code` `public` `static` `void` `main(String[] args)` `{` ` ` `String S = ` `"abcd1111aabc"` `;` ` ` `char` `K = ` `'1'` `;` ` ` `// Function call` ` ` `System.out.print(length_substring(S, K));` `}` `}` `// This code is contributed by Chitranayal` |

## Python3

`# Python3 program for the above approach` `# Function to find the length of` `# longest sub-string having all` `# characters same as character K` `def` `length_substring(S, K):` ` ` ` ` `# Initialize variables` ` ` `curr_cnt ` `=` `0` ` ` `prev_cnt ` `=` `0` ` ` `max_len ` `=` `0` ` ` `# Iterate till size of string` ` ` `for` `i ` `in` `range` `(` `len` `(S)):` ` ` `# Check if current character is K` ` ` `if` `(S[i] ` `=` `=` `K):` ` ` `curr_cnt ` `+` `=` `1` ` ` `else` `:` ` ` `prev_cnt ` `=` `max` `(prev_cnt,` ` ` `curr_cnt)` ` ` `curr_cnt ` `=` `0` ` ` `prev_cnt ` `=` `max` `(prev_cnt, curr_cnt)` ` ` `# Assingning the max` ` ` `# value to max_len` ` ` `max_len ` `=` `prev_cnt` ` ` `return` `max_len` `# Driver code` `if` `__name__ ` `=` `=` `'__main__'` `:` ` ` ` ` `S ` `=` `"abcd1111aabc"` ` ` `K ` `=` `'1'` ` ` `# Function call` ` ` `print` `(length_substring(S, K))` `# This code is contributed by mohit kumar 29` |

## C#

`// C# program for the above approach` `using` `System;` `class` `GFG{` `// Function to find the length of` `// longest sub-string having all` `// characters same as character K` `static` `int` `length_substring(` `string` `S, ` `char` `K)` `{` ` ` ` ` `// Initialize variables` ` ` `int` `curr_cnt = 0, prev_cnt = 0, max_len;` ` ` ` ` `// Iterate till size of string` ` ` `for` `(` `int` `i = 0; i < S.Length; i++)` ` ` `{` ` ` ` ` `// Check if current character is K` ` ` `if` `(S[i] == K)` ` ` `{` ` ` `curr_cnt += 1;` ` ` `}` ` ` `else` ` ` `{` ` ` `prev_cnt = Math.Max(prev_cnt,` ` ` `curr_cnt);` ` ` `curr_cnt = 0;` ` ` `}` ` ` `}` ` ` `prev_cnt = Math.Max(prev_cnt, curr_cnt);` ` ` ` ` `// Assingning the max` ` ` `// value to max_len` ` ` `max_len = prev_cnt;` ` ` `return` `max_len;` `}` `// Driver code` `static` `public` `void` `Main()` `{` ` ` `string` `S = ` `"abcd1111aabc"` `;` ` ` `char` `K = ` `'1'` `;` ` ` ` ` `// Function call` ` ` `Console.WriteLine(length_substring(S, K));` `}` `}` `// This code is contributed by rag2127` |

## Javascript

`<script>` `// Javascript program for` `// the above approach` `// Function to find the length of` `// longest sub-string having all` `// characters same as character K` `function` `length_substring(S, K)` `{` ` ` ` ` `// Initialize variables` ` ` `let curr_cnt = 0, prev_cnt = 0,` ` ` `max_len;` ` ` ` ` `// Iterate till size of string` ` ` `for` `(let i = 0; i < S.length; i++)` ` ` `{` ` ` ` ` `// Check if current character is K` ` ` `if` `(S[i] == K)` ` ` `{` ` ` `curr_cnt += 1;` ` ` `}` ` ` `else` ` ` `{` ` ` `prev_cnt = Math.max(prev_cnt,` ` ` `curr_cnt);` ` ` `curr_cnt = 0;` ` ` `}` ` ` `}` ` ` ` ` `prev_cnt = Math.max(prev_cnt,` ` ` `curr_cnt);` ` ` ` ` `// Assingning the max` ` ` `// value to max_len` ` ` `max_len = prev_cnt;` ` ` ` ` `return` `max_len;` `}` `// Driver code` `let S = ` `"abcd1111aabc"` `;` `let K = ` `'1'` `;` `// Function call` `document.write(length_substring(S, K));` `// This code is contributed by avanitrachhadiya2155` `</script>` |

**Output:**

4

**Time Complexity: **O(N) **Auxiliary Space: **O(1)