# Count of increasing substrings in given String

• Last Updated : 17 Nov, 2021

Given string str of length N, the task is to print the number of substrings in which every character’s ASCII value is greater or equal to the ASCII value of the previous character. The substrings must at least be of length 2.

Example

Input: str = “bcdabc”
Output: 6
Explanation: The 6 substrings with alphabets having greater ASCII value than the previous character and length at least 2 are bc, bcd, cd, ab, abc, bc

Input: str = “cegxza”
Output: 10

Naive Approach: The above problem can be iterating the string and counting increasing ASCII value substrings starting at every index.
Time Complexity: O(N^2)

Approach: An efficient approach for the given problem would be to iterate the string and use a mathematical calculation to find all possible increasing ASCII value substrings in a larger substring. Follow the approach below to solve the problem:

• Initialize pointers left and right to 0
• Initialize a variable ans to store the answer
• Iterate the string until the right pointer is less than the length of the string:
• Use a while loop to iterate using the right pointer until str[right] >= str[right – 1] and right < str.length()
• Calculate the number of substrings having increasing ASCII value by adding initializing len = right – left, then adding then value of (len * (len + 1) / 2) – len to ans
• Make left = right and the right pointer will get incremented for the next iteration
• Return ans as our result

Below is the implementation of the above approach:

## C++

 `// C++ code for the above approach``#include ``using` `namespace` `std;` `// Function to count number of substrings``// with increasing ascii values``int` `countIncSub(string str)``{` `    ``// Initialize left and right pointers``    ``int` `left = 0, right = 1;` `    ``// Initialize length of the string str``    ``int` `l = str.length();` `    ``// Initialize a variable to store answer``    ``int` `ans = 0;` `    ``// Iterate the string``    ``for` `(; right < l; right++)``    ``{` `        ``// Iterate the while loop until the``        ``// string has increasing ASCII value``        ``while` `(right < l && str[right] >= str[right - 1])``        ``{` `            ``right++;``        ``}` `        ``// Calculate length of longest``        ``// substring found starting from left``        ``int` `len = right - left;` `        ``// Calculate the number of substrings``        ``// with length at least 2 and add it``        ``// to the ans``        ``ans += (len * (len + 1)) / 2 - len;` `        ``// Update left equal to right``        ``left = right;``    ``}` `    ``// Return the answer``    ``return` `ans;``}` `int` `main()``{` `    ``// Initialize the string str``    ``string str = ``"cegxza"``;` `    ``// Call the function and``    ``// print the result``    ``cout << (countIncSub(str));``}` `// This code is contributed by Potta Lokesh`

## Java

 `// Java implementation for the above approach` `import` `java.io.*;``import` `java.util.*;` `// Driver code``class` `GFG {` `    ``// Function to count number of substrings``    ``// with increasing ascii values``    ``public` `static` `int` `countIncSub(String str)``    ``{` `        ``// Initialize left and right pointers``        ``int` `left = ``0``, right = ``1``;` `        ``// Initialize length of the string str``        ``int` `l = str.length();` `        ``// Initialize a variable to store answer``        ``int` `ans = ``0``;` `        ``// Iterate the string``        ``for` `(; right < l; right++) {` `            ``// Iterate the while loop until the``            ``// string has increasing ASCII value``            ``while` `(right < l``                   ``&& str.charAt(right)``                          ``>= str.charAt(right - ``1``)) {` `                ``right++;``            ``}` `            ``// Calculate length of longest``            ``// substring found starting from left``            ``int` `len = right - left;` `            ``// Calculate the number of substrings``            ``// with length at least 2 and add it``            ``// to the ans``            ``ans += (len * (len + ``1``)) / ``2` `- len;` `            ``// Update left equal to right``            ``left = right;``        ``}` `        ``// Return the answer``        ``return` `ans;``    ``}` `    ``public` `static` `void` `main(String[] args)``    ``{` `        ``// Initialize the string str``        ``String str = ``"cegxza"``;` `        ``// Call the function and``        ``// print the result``        ``System.out.println(countIncSub(str));``    ``}``}`

## Python3

 `# Python code for the above approach` `# Function to count number of substrings``# with increasing ascii values``def` `countIncSub(``str``):` `    ``# Initialize left and right pointers``    ``left ``=` `0``    ``right ``=` `1` `    ``# Initialize length of the string str``    ``l ``=` `len``(``str``)` `    ``# Initialize a variable to store answer``    ``ans ``=` `0` `    ``# Iterate the string``    ``for` `right ``in` `range``(``1``, l):` `        ``# Iterate the while loop until the``        ``# string has increasing ASCII value``        ``while` `(right < l ``and` `str``[right] >``=` `str``[right ``-` `1``]):``            ``right ``+``=` `1` `        ``# Calculate length of longest``        ``# substring found starting from left``        ``length ``=` `right ``-` `left` `        ``# Calculate the number of substrings``        ``# with length at least 2 and add it``        ``# to the ans``        ``ans ``+``=` `(length ``*` `(length ``+` `1``)) ``/``/` `2` `-` `length` `        ``# Update left equal to right``        ``left ``=` `right` `    ``# Return the answer``    ``return` `ans` `# Driver Code``# Initialize the string str``str` `=` `"cegxza"` `# Call the function and``# print the result``print``(countIncSub(``str``))` `# This code is contributed by Saurabh Jaiswal`

## C#

 `// C# implementation for the above approach``using` `System;``using` `System.Collections;` `// Driver code``class` `GFG {` `    ``// Function to count number of substrings``    ``// with increasing ascii values``    ``static` `int` `countIncSub(``string` `str)``    ``{``        ``// Initialize left and right pointers``        ``int` `left = 0, right = 1;` `        ``// Initialize length of the string str``        ``int` `l = str.Length;` `        ``// Initialize a variable to store answer``        ``int` `ans = 0;` `        ``// Iterate the string``        ``for` `(; right < l; right++) {` `            ``// Iterate the while loop until the``            ``// string has increasing ASCII value``            ``while` `(right < l``                   ``&& str[right]``                          ``>= str[right - 1]) {` `                ``right++;``            ``}` `            ``// Calculate length of longest``            ``// substring found starting from left``            ``int` `len = right - left;` `            ``// Calculate the number of substrings``            ``// with length at least 2 and add it``            ``// to the ans``            ``ans += (len * (len + 1)) / 2 - len;` `            ``// Update left equal to right``            ``left = right;``        ``}` `        ``// Return the answer``        ``return` `ans;``    ``}` `    ``public` `static` `void` `Main()``    ``{``      ` `        ``// Initialize the string str``        ``string` `str = ``"cegxza"``;` `        ``// Call the function and``        ``// print the result``        ``Console.Write(countIncSub(str));``    ``}``}``// This code is contributed by Samim Hossain Mondal`

## Javascript

 ``
Output:
`10`

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

My Personal Notes arrow_drop_up