Self Permutation

• Time : $O(n)$
• Space : $O(n)$

int Solution::permuteStrings(string A, string B) {
    if(A.length() != B.length()) return 0;
    unordered_map<char, int> freq;
    for(auto a : A) freq[a]++;
    for(auto b : B) if(--freq[b] == 0) freq.erase(b);
    return freq.empty();
}