242. Valid Anagram 🌟

Given two strings s and t, return true if t is an anagram of s, and false otherwise.

O(N logN) Time and constant space

• sort both strings and compare them.
• if they are equal, return true else false.

Code

class Solution {
public:
    bool isAnagram(string s, string t) {
        sort(s.begin(),s.end());
        sort(t.begin(),t.end());
        return s==t?true:false;
    }
};

O(N) Time and O(N)=O(26) constant space

• We store frequency of each character in a hash table.
• Decrement the frequency of each character in hash table which is in the t.
• If any frequency is not zero, return false.

Code

class Solution {
public:
    bool isAnagram(string s, string t) {
        vector<int> a(26,0);
        if(s.size()!=t.size()) return false;
        for(auto &x:s){
            a[x-'a']++;
        }
        for(auto &x:t){
            --a[x-'a'];
        }
        for(auto &x:a){
            if(x>=1) return false;
        }
        return true;
    }
};

Only 2 loops

• first confirm sizes of both strings is same.
• We can avoid 3rd loop by checking if the frequency of each character less than 0 then return false.
• return true by default.

Code

class Solution {
public:
    bool isAnagram(string s, string t) {
        vector<int> a(26,0);
        if(s.size()!=t.size()) return false;
        for(auto &x:s){
            a[x-'a']++;
        }
        for(auto &x:t){
            if(--a[x-'a']<0) return false;
        }
        return true;
    }
};