# Find All Anagrams in a String in C++

C++Server Side ProgrammingProgramming

Suppose we have a string s and a non-empty string p, we have to find all the start indices of p's anagrams in s. The strings consist of lowercase letters only and the length of both strings s and p will not be larger than 20 and 100. So for example, if s: "cbaebabacd" p: "abc", then the output will be [0, 6], at index 0, it is “cba”, and another is “bac”, these are the anagrams of “abc”.

To solve this, we will follow these steps −

• Define a map m, n := size of s, set left := 0, right := 0, counter := size of p

• define an array ans

• store the frequency of characters in p into the map m

• for right := 0 to n – 1

• if m has s[right] and m[s[right]] is non zero, then decrease m[s[right]] by 1, decrease counter by 1 and if counter = 0, then insert left into ans

• otherwise

• while left < right,

• if s[left] is not present in m, then increase counter by 1, and increase m[s[left]] by 1

• increase left by 1

• if m has s[right] and m[s[right]] is non zero, then decrease right by 1, and come out from the loop

• if m has no s[left], then set left := right + 1

• return ans

## Example(C++)

Let us see the following implementation to get a better understanding −

Live Demo

#include <bits/stdc++.h>
using namespace std;
void print_vector(vector<auto> v){
cout << "[";
for(int i = 0; i<v.size(); i++){
cout << v[i] << ", ";
}
cout << "]"<<endl;
}
class Solution {
public:
vector<int> findAnagrams(string s, string p) {
map <char, int> m;
int n = s.size();
int left = 0, right = 0;
int counter = p.size();
vector <int> ans;
for(int i = 0; i < p.size(); i++) m[p[i]]++;
for(int right = 0; right < n; right++){
if(m.find(s[right]) != m.end() && m[s[right]]){
m[s[right]]--;
counter--;
if(counter == 0)ans.push_back(left);
} else {
while(left<right){
if(m.find(s[left]) != m.end()) {
counter++;
m[s[left]]++;
}
left++;
if(m.find(s[right]) != m.end() && m[s[right]]){
right--;
break;
}
}
if(m.find(s[left])==m.end())left = right + 1;
}
}
return ans;
}
};
main(){
Solution ob;
print_vector(ob.findAnagrams("cbaebabacd", "abc")) ;
}

## Input

"cbaebabacd"
"abc"

## Output

[0, 6, ]
Published on 17-Mar-2020 06:17:12