# Count substrings that starts with character X and ends with character Y

Given a string str of n lowercase characters, the task is to count the number of substrings of str starting with character X and ending with character Y.

Examples:

```Input: str = "abbcaceghcak"
x = 'a', y = 'c'
Output: 5
abbc, abbcac, ac, abbcaceghc, aceghc

Input: str = "geeksforgeeks"
x = 'g', y = 'e'
Output: 6
```

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

Approach:

• Initialize two counters i.e. tot_count to count the total number of substrings and count_x to count the number of strings that start with X.
• Start traversing the string.
• If the current character is X then increment the count of count_x.
• If the current character is Y, it means a string ends at Y so increment the count of tot_count i.e.
`tot_count = tot_count + count_x`

It means that if there exists a Y then it will make a substring with all the X occurs before Y in the string. So, add the count of X to the total count.

Below is the implementation of above approach:

## C++

 `// C++ implementation to count substrings ` `// starting with character X and ending ` `// with character Y ` `#include ` `using` `namespace` `std; ` ` `  `// function to count substrings starting with ` `// character X and ending with character Y ` `int` `countSubstr(string str, ``int` `n, ` `                ``char` `x, ``char` `y) ` `{ ` `    ``// to store total count of ` `    ``// required substrings ` `    ``int` `tot_count = 0; ` ` `  `    ``// to store count of character 'x' ` `    ``// up to the point the string 'str' ` `    ``// has been traversed so far ` `    ``int` `count_x = 0; ` ` `  `    ``// traverse 'str' form left to right ` `    ``for` `(``int` `i = 0; i < n; i++) { ` ` `  `        ``// if true, increment 'count_x' ` `        ``if` `(str[i] == x) ` `            ``count_x++; ` ` `  `        ``// if true accumulate 'count_x' ` `        ``// to 'tot_count' ` `        ``if` `(str[i] == y) ` `            ``tot_count += count_x; ` `    ``} ` ` `  `    ``// required count ` `    ``return` `tot_count; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``string str = ``"abbcaceghcak"``; ` `    ``int` `n = str.size(); ` `    ``char` `x = ``'a'``, y = ``'c'``; ` ` `  `    ``cout << ``"Count = "` `         ``<< countSubstr(str, n, x, y); ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java implementation to count  ` `// substrings starting with  ` `// character X and ending ` `// with character Y ` `import` `java.util.*; ` `import` `java.lang.*; ` `import` `java.io.*; ` ` `  `class` `GFG ` `{ ` `// function to count substrings  ` `// starting with character X and ` `// ending with character Y ` `static` `int` `countSubstr(String str, ``int` `n, ` `                       ``char` `x, ``char` `y) ` `{ ` `    ``// to store total count of ` `    ``// required substrings ` `    ``int` `tot_count = ``0``; ` ` `  `    ``// to store count of character  ` `    ``// 'x' up to the point the  ` `    ``// string 'str' has been ` `    ``// traversed so far ` `    ``int` `count_x = ``0``; ` ` `  `    ``// traverse 'str' form ` `    ``// left to right ` `    ``for` `(``int` `i = ``0``; i < n; i++) ` `    ``{ ` ` `  `        ``// if true, increment 'count_x' ` `        ``if` `(str.charAt(i) == x) ` `            ``count_x++; ` ` `  `        ``// if true accumulate 'count_x' ` `        ``// to 'tot_count' ` `        ``if` `(str.charAt(i) == y) ` `            ``tot_count += count_x; ` `    ``} ` ` `  `    ``// required count ` `    ``return` `tot_count; ` `} ` ` `  `// Driver code ` `public` `static` `void` `main(String args[]) ` `{ ` `    ``String str = ``"abbcaceghcak"``; ` `    ``int` `n = str.length(); ` `    ``char` `x = ``'a'``, y = ``'c'``; ` ` `  `    ``System.out.print (``"Count = "` `+ ` `       ``countSubstr(str, n, x, y)); ` `} ` `} ` ` `  `// This code is contributed ` `// by Subhadeep `

## Python3

 `# Python 3 implementation to count substrings  ` `# starting with character X and ending  ` `# with character Y  ` ` `  `# function to count substrings starting with  ` `# character X and ending with character Y  ` `def` `countSubstr(``str``, n, x, y): ` ` `  `    ``# to store total count of  ` `    ``# required substrings  ` `    ``tot_count ``=` `0` ` `  `    ``# to store count of character 'x'  ` `    ``# up to the point the string 'str'  ` `    ``# has been traversed so far  ` `    ``count_x ``=` `0` ` `  `    ``# traverse 'str' form left to right ` `    ``for` `i ``in` `range``(n): ` ` `  `        ``# if true, increment 'count_x'  ` `        ``if` `str``[i] ``=``=` `x: ` `            ``count_x ``+``=` `1` ` `  `        ``# if true accumulate 'count_x'  ` `        ``# to 'tot_count'  ` `        ``if` `str``[i] ``=``=` `y: ` `            ``tot_count ``+``=` `count_x ` `     `  `    ``# required count ` `    ``return` `tot_count ` ` `  `# Driver Code ` `str` `=` `'abbcaceghcak'` `n ``=` `len``(``str``) ` `x, y ``=` `'a'``, ``'c'` `print``(``'Count ='``, countSubstr(``str``, n, x, y)) ` ` `  `# This code is contributed SamyuktaSHegde `

## C#

 `// C# implementation to count substrings  ` `// starting with character X and ending ` `// with character Y ` `using` `System; ` ` `  `class` `GFG ` `{ ` `// function to count substrings starting  ` `// with character X and ending with character Y ` `static` `int` `countSubstr(``string` `str, ``int` `n, ` `                       ``char` `x, ``char` `y) ` `{ ` `    ``// to store total count of ` `    ``// required substrings ` `    ``int` `tot_count = 0; ` ` `  `    ``// to store count of character 'x' up  ` `    ``// to the point the string 'str' has  ` `    ``// been traversed so far ` `    ``int` `count_x = 0; ` ` `  `    ``// traverse 'str' form left to right ` `    ``for` `(``int` `i = 0; i < n; i++) ` `    ``{ ` ` `  `        ``// if true, increment 'count_x' ` `        ``if` `(str[i] == x) ` `            ``count_x++; ` ` `  `        ``// if true accumulate 'count_x' ` `        ``// to 'tot_count' ` `        ``if` `(str[i] == y) ` `            ``tot_count += count_x; ` `    ``} ` ` `  `    ``// required count ` `    ``return` `tot_count; ` `} ` ` `  `// Driver code ` `public` `static` `void` `Main() ` `{ ` `    ``string` `str = ``"abbcaceghcak"``; ` `    ``int` `n = str.Length; ` `    ``char` `x = ``'a'``, y = ``'c'``; ` ` `  `    ``Console.Write(``"Count = "` `+ ` `    ``countSubstr(str, n, x, y)); ` `} ` `} ` ` `  `// This code is contributed ` `// by Akanksha Rai `

## PHP

 `

Output:

```Count = 5
```

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