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Find max length odd parity substring
• Last Updated : 20 Nov, 2019

Given a binary string str, the task is to find the maximum length of the sub-string of str that has odd parity. A binary string is said be odd parity if it contains odd number of 1s.

Examples:

Input: str = “1001110”
Output: 6
“001110” is the valid sub-string.

Input: str = “101101”
Output: 5

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach:

1. Count the number of 1s in the given string and store it in a variable cnt.
2. If cnt = 0 then there is no sub-string possible with odd parity so the result will be 0.
3. If cnt is odd then the result will be the complete string.
4. Now for the case when cnt is even and > 0, the required sub-string will either start at index 0 and end just before the last occurrence of 1 or start just after the first occurrence of 1 and end at the end of the given string.
5. Choose the one with the greater length among the two sub-strings in the previous step.

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach ``#include ``using` `namespace` `std;`` ` `    ``// finds the index of character of string``    ``int` `indexOf(string s, ``char` `c, ``int` `i)``    ``{``        ``for``(; i < s.length(); i++)``        ``if``(s[i] == c)``        ``return` `i;``         ` `        ``return` `-1;``    ``}``     ` `    ``// finds the last index of character of string``    ``int` `lastIndexOf(string s,``char` `c,``int` `i)``    ``{``        ``for``(; i >= 0; i--)``        ``if``(s[i] == c)``            ``return` `i;``         ` `        ``return` `-1;``    ``}`` ` `    ``// Function to return the maximum ``    ``// length of the sub-string which ``    ``// contains odd number of 1s ``    ``int` `maxOddParity(string str, ``int` `n) ``    ``{ `` ` `        ``// Find the count of 1s in ``        ``// the given string ``        ``int` `cnt = 0; ``        ``for` `(``int` `i = 0; i < n; i++) ``            ``if` `(str[i] == ``'1'``) ``                ``cnt++; `` ` `        ``// If there are only 0s in the string ``        ``if` `(cnt == 0) ``            ``return` `0; `` ` `        ``// If the count of 1s is odd then ``        ``// the complete string has odd parity ``        ``if` `(cnt % 2 == 1) ``            ``return` `n; `` ` `        ``// Index of the first and the second ``        ``// occurrences of '1' in the string ``        ``int` `firstOcc = indexOf(str,``'1'``,0); ``        ``int` `secondOcc = indexOf(str,``'1'``, firstOcc + 1); `` ` `        ``// Index of the last and the second last ``        ``// occurrences of '1' in the string ``        ``int` `lastOcc = lastIndexOf(str,``'1'``,str.length()-1); ``        ``int` `secondLastOcc = lastIndexOf(str,``'1'``, lastOcc - 1); `` ` `        ``// Result will the sub-string ending just ``        ``// before the last occurrence of '1' or the ``        ``// sub-string starting just after the first ``        ``// occurrence of '1' ``        ``// choose the one with the maximum length ``        ``return` `max(lastOcc, n - firstOcc - 1); ``    ``} `` ` `    ``// Driver code ``    ``int` `main() ``    ``{ ``        ``string str = ``"101101"``; ``        ``int` `n = str.length(); ``        ``cout<<(maxOddParity(str, n)); ``    ``} `` ` `// This code is contributed by Arnab Kundu`

## Java

 `// Java implementation of the approach``public` `class` `GFG {`` ` `    ``// Function to return the maximum``    ``// length of the sub-string which``    ``// contains odd number of 1s``    ``static` `int` `maxOddParity(String str, ``int` `n)``    ``{`` ` `        ``// Find the count of 1s in``        ``// the given string``        ``int` `cnt = ``0``;``        ``for` `(``int` `i = ``0``; i < n; i++)``            ``if` `(str.charAt(i) == ``'1'``)``                ``cnt++;`` ` `        ``// If there are only 0s in the string``        ``if` `(cnt == ``0``)``            ``return` `0``;`` ` `        ``// If the count of 1s is odd then``        ``// the complete string has odd parity``        ``if` `(cnt % ``2` `== ``1``)``            ``return` `n;`` ` `        ``// Index of the first and the second``        ``// occurrences of '1' in the string``        ``int` `firstOcc = str.indexOf(``'1'``);``        ``int` `secondOcc = str.indexOf(``'1'``, firstOcc + ``1``);`` ` `        ``// Index of the last and the second last``        ``// occurrences of '1' in the string``        ``int` `lastOcc = str.lastIndexOf(``'1'``);``        ``int` `secondLastOcc = str.lastIndexOf(``'1'``, lastOcc - ``1``);`` ` `        ``// Result will the sub-string ending just``        ``// before the last occurrence of '1' or the``        ``// sub-string starting just after the first``        ``// occurrence of '1'``        ``// choose the one with the maximum length``        ``return` `Math.max(lastOcc, n - firstOcc - ``1``);``    ``}`` ` `    ``// Driver code``    ``public` `static` `void` `main(String[] args)``    ``{``        ``String str = ``"101101"``;``        ``int` `n = str.length();``        ``System.out.print(maxOddParity(str, n));``    ``}``}`

## Python3

 `# Python3 implementation of the approach`` ` `# Function to return the maximum``# length of the sub-string which``# contains odd number of 1s``def` `maxOddParity(string, n):`` ` `    ``# Find the count of 1s in``    ``# the given string``    ``cnt ``=` `0``    ``for` `i ``in` `range``(n):``        ``if` `string[i] !``=` `'1'``:``            ``cnt ``+``=` `1`` ` `    ``# If there are only 0s in the string``    ``if` `cnt ``=``=` `0``:``        ``return` `0`` ` `    ``# If the count of 1s is odd then``    ``# the complete string has odd parity``    ``if` `cnt ``%` `2` `=``=` `1``:``        ``return` `n`` ` `    ``# Index of the first and the second``    ``# occurrences of '1' in the string``    ``firstOcc ``=` `string.index(``'1'``)``    ``secondOcc ``=` `string.index(``'1'``, firstOcc ``+` `1``)`` ` `    ``# Index of the last and the second last``    ``# occurrences of '1' in the string``    ``lastOcc ``=` `string.rindex(``'1'``)``    ``secondLastOcc ``=` `string.rindex(``'1'``, ``0``, lastOcc)`` ` `    ``# Result will the sub-string ending just``    ``# before the last occurrence of '1' or the``    ``# sub-string starting just after the first``    ``# occurrence of '1'``    ``# choose the one with the maximum length``    ``return` `max``(lastOcc, n ``-` `firstOcc ``-` `1``)`` ` `# Driver Code``if` `__name__ ``=``=` `"__main__"``:``    ``string ``=` `"101101"``    ``n ``=` `len``(string)``    ``print``(maxOddParity(string, n))`` ` `# This code is contributed by``# sanjeev2552`

## C#

 `// C# implementation of the above approach ``using` `System;`` ` `class` `GFG ``{`` ` `    ``// Function to return the maximum``    ``// length of the sub-string which``    ``// contains odd number of 1s``    ``static` `int` `maxOddParity(String str, ``int` `n)``    ``{`` ` `        ``// Find the count of 1s in``        ``// the given string``        ``int` `cnt = 0;``        ``for` `(``int` `i = 0; i < n; i++)``            ``if` `(str[i] == ``'1'``)``                ``cnt++;`` ` `        ``// If there are only 0s in the string``        ``if` `(cnt == 0)``            ``return` `0;`` ` `        ``// If the count of 1s is odd then``        ``// the complete string has odd parity``        ``if` `(cnt % 2 == 1)``            ``return` `n;`` ` `        ``// Index of the first and the second``        ``// occurrences of '1' in the string``        ``int` `firstOcc = str.IndexOf(``'1'``);``        ``int` `secondOcc = str.IndexOf(``'1'``, firstOcc + 1);`` ` `        ``// Index of the last and the second last``        ``// occurrences of '1' in the string``        ``int` `lastOcc = str.LastIndexOf(``'1'``);``        ``int` `secondLastOcc = str.LastIndexOf(``'1'``, lastOcc - 1);`` ` `        ``// Result will the sub-string ending just``        ``// before the last occurrence of '1' or the``        ``// sub-string starting just after the first``        ``// occurrence of '1'``        ``// choose the one with the maximum length``        ``return` `Math.Max(lastOcc, n - firstOcc - 1);``    ``}`` ` `    ``// Driver code``    ``public` `static` `void` `Main(String[] args)``    ``{``        ``String str = ``"101101"``;``        ``int` `n = str.Length;``        ``Console.WriteLine(maxOddParity(str, n));``    ``}``}`` ` `/* This code contributed by PrinciRaj1992 */`
Output:
```5
```

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