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Sum of frequencies of characters of a string present in another string
  • Last Updated : 24 Feb, 2021

Given two strings S1 and S2 of lengths M and N respectively, the task is to calculate the sum of the frequencies of the characters of string S1 in the string S2.

Examples:

Input: S1 = “pPKf”, S2 = “KKKttsdppfP”
Output: 7
Explanation:
The character ‘p’ occurs twice in the string S2.
The character ‘P’ occurs once in the string S2.
The character ‘K’ occurs thrice in the string S2.
The character ‘f’ occurs once in the string S2.
Therefore, in total, characters of the string S1 occurs 7 times in the string S2.

Input: S1 = “geEksFOR”, S2 = “GeEksforgeEKS”
Output: 7

Naive Approach: The simplest approach is to iterate over each character of the string S1, count its frequency in the string S2
Time Complexity: O(N2)
Auxiliary Space: O(1)

Efficient Approach: The above approach can be optimized by using Hashing. Follow the steps below to solve the problem:



Below is the implementation of the above approach:

C++

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// CPP program for the above approach
#include<bits/stdc++.h>
using namespace std;
 
// Function to find sum of frequencies
// of characters of S1 present in S2
void countTotalFrequencies(string S1, string S2)
{
 
  // Insert all characters of
  // string S1 in the set
  set<char> bset;
  for(auto x:S1)
    bset.insert(x);
  int count = 0;
 
  // Traverse the string S2
  for (auto x: S2)
  {
 
    // Check if X is present
    // in bset or not
    if (bset.find(x) != bset.end())
 
      // Increment count by 1
      count += 1;
  }
 
  // Finally, print the count
  cout << count << endl;
 
}
 
// Driver Code
int main()
{
   
  // Given strings
  string S1 = "geEksFOR";
  string S2 = "GeEksforgeEKS";
 
  countTotalFrequencies(S1, S2);
 
}
 
// This code is contributed by ipg2016107.

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Python3

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# Python3 program for the above approach
 
# Function to find sum of frequencies
# of characters of S1 present in S2
def countTotalFrequencies(S1, S2):
 
    # Insert all characters of
    # string S1 in the set
    bset = set(S1)
    count = 0
 
    # Traverse the string S2
    for x in S2:
 
        # Check if X is present
        # in bset or not
        if x in bset:
 
            # Increment count by 1
            count += 1
 
    # Finally, print the count
    print(count)
 
# Driver Code
 
# Given strings
S1 = "geEksFOR"
S2 = "GeEksforgeEKS"
 
countTotalFrequencies(S1, S2)

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Output: 

7

 

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

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