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Count number of substrings of a string consisting of same characters
  • Difficulty Level : Medium
  • Last Updated : 28 May, 2021

Given a string. The task is to find out the numbers of substrings consisting of the same characters.

Examples: 

Input: abba 
Output:
The desired substrings are {a}, {b}, {b}, {a}, {bb}

Input: bbbcbb 
Output: 10 
 

Approach : It is known for a string of length n, there are a total of n*(n+1)/2 number of substrings.
Let’s initialize the result to 0. Traverse the string and find the number of consecutive element(let’s say count) of same characters. Whenever we find another character, increment the result by count*(count+1)/2, set count to 1 and from that index, repeat the above process.
Remember, for each different character, the number of our desired substring is 1.



Below is the implementation of the above approach:  

C++




// C++ implementation
// of the above approach
#include <bits/stdc++.h>
using namespace std;
 
// Function to return the
// number of substrings of
// same characters
void findNumbers(string s)
{
    // Size of the string
    int n = s.size();
 
    // Initialize count to 1
    int count = 1;
    int result = 0;
 
    // Initialize left to 0 and
    // right to 1 to traverse the
    // string
    int left = 0;
    int right = 1;
 
    while (right < n) {
 
        // Checking if consecutive
        // characters are same and
        // increment the count
        if (s[left] == s[right]) {
            count++;
        }
 
        // When we encounter a
        // different characters
        else {
 
            // Increment the result
            result += count * (count + 1) / 2;
 
            // To repeat the whole
            // process set left equals
            // right and count variable to 1
            left = right;
            count = 1;
        }
 
        right++;
    }
 
    // Store the final
    // value of result
    result += count * (count + 1) / 2;
 
    cout << result << endl;
}
 
// Driver code
int main()
{
    string s = "bbbcbb";
 
    findNumbers(s);
}

Java




// Java implementation of the approach
class GFG
{
     
    // Function to return the
    // number of substrings of
    // same characters
    static void findNumbers(String s)
    {
        // Size of the string
        int n = s.length();
     
        // Initialize count to 1
        int count = 1;
        int result = 0;
     
        // Initialize left to 0 and
        // right to 1 to traverse the
        // string
        int left = 0;
        int right = 1;
     
        while (right < n)
        {
     
            // Checking if consecutive
            // characters are same and
            // increment the count
            if (s.charAt(left) == s.charAt(right))
            {
                count++;
            }
     
            // When we encounter a
            // different characters
            else
            {
     
                // Increment the result
                result += count * (count + 1) / 2;
     
                // To repeat the whole
                // process set left equals
                // right and count variable to 1
                left = right;
                count = 1;
            }
     
            right++;
        }
     
        // Store the final
        // value of result
        result += count * (count + 1) / 2;
     
        System.out.println(result);
    }
 
    // Driver code
    public static void main (String[] args)
    {
        String s = "bbbcbb";
 
        findNumbers(s);
    }
}
 
// This code is contributed by AnkitRai01

Python3




# Python3 implementation of the above approach
 
# Function to return the number of
# substrings of same characters
def findNumbers(s):
     
    # Size of the string
    n = len(s)
 
    # Initialize count to 1
    count = 1
    result = 0
 
    # Initialize left to 0 and right to 1
    # to traverse the string
    left = 0
    right = 1
 
    while (right < n):
 
        # Checking if consecutive
        # characters are same and
        # increment the count
        if (s[left] == s[right]):
            count += 1
 
        # When we encounter a
        # different characters
        else:
 
            # Increment the result
            result += count * (count + 1) // 2
 
            # To repeat the whole
            # process set left equals
            # right and count variable to 1
            left = right
            count = 1
 
        right += 1
 
    # Store the final value of result
    result += count * (count + 1) // 2
 
    print(result)
 
# Driver code
s = "bbbcbb"
 
findNumbers(s)
 
# This code is contributed by Mohit Kumar

C#




// C# implementation of the approach
using System;
 
class GFG
{
    // Function to return the
    // number of substrings of
    // same characters
    static void findNumbers(String s)
    {
        // Size of the string
        int n = s.Length;
 
        // Initialize count to 1
        int count = 1;
        int result = 0;
 
        // Initialize left to 0 and
        // right to 1 to traverse the
        // string
        int left = 0;
        int right = 1;
 
        while (right < n)
        {
            // Checking if consecutive
            // characters are same and
            // increment the count
            if (s[left] == s[right])
                count++;
 
            // When we encounter a
            // different characters
            else
            {
                // Increment the result
                result += count * (count + 1) / 2;
 
                // To repeat the whole
                // process set left equals
                // right and count variable to 1
                left = right;
                count = 1;
            }
            right++;
        }
 
        // Store the final
        // value of result
        result += count * (count + 1) / 2;
 
        Console.WriteLine(result);
    }
 
    // Driver code
    public static void Main(String[] args)
    {
        String s = "bbbcbb";
 
        findNumbers(s);
    }
}
 
// This code is contibuted by
// sanjeev2552

Javascript




<script>
 
// Javascript implementation
// of the above approach
 
// Function to return the
// number of substrings of
// same characters
function findNumbers(s)
{
     
    // Size of the string
    var n = s.length;
 
    // Initialize count to 1
    var count = 1;
    var result = 0;
 
    // Initialize left to 0 and
    // right to 1 to traverse the
    // string
    var left = 0;
    var right = 1;
 
    while (right < n)
    {
         
        // Checking if consecutive
        // characters are same and
        // increment the count
        if (s[left] == s[right])
        {
            count++;
        }
 
        // When we encounter a
        // different characters
        else
        {
             
            // Increment the result
            result += parseInt(count * (count + 1) / 2);
 
            // To repeat the whole
            // process set left equals
            // right and count variable to 1
            left = right;
            count = 1;
        }
        right++;
    }
 
    // Store the final
    // value of result
    result += parseInt(count * (count + 1) / 2);
 
    document.write(result);
}
 
// Driver code
var s = "bbbcbb";
 
findNumbers(s);
 
// This code is contributed by itsok
 
</script>
Output: 
10

 

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