Valid Anagram

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Description

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

An Anagram is a word or phrase formed by rearranging the letters of a different word or phrase, typically using all the original letters exactly once.

Example 1:

• Input: s = "anagram", t = "nagaram"
• Output: true

Example 2:

• Input: s = "rat", t = "car"
• Output: false

Constraints:

• 1 <= s.length, t.length <= 5 * 10^4
• s and t consist of lowercase English letters.

Solution

Hash Map

• Assuming that the string contains only lowercase letters, use an array of length 26 as a hash table to keep track of the number of times a letter appears.
• For s, add the number of letters to the hash table.
• For t, reduce the number of corresponding letters in the hash table.
• Finally, from a to z statistics whether there is not 0 cases, if so, then return false, otherwise return true.

class Solution {
public:
    bool isAnagram(string s, string t) {
        if (s.length() != t.length()) return false;
        int record[26] = {0};
        for (int i = 0; i < s.size(); i++) {
            record[s[i] - 'a']++;
            record[t[i] - 'a']--;
        }
        //If any element of the record array is not 0, the strings s and t must be either more or less characters.
        for (int i = 0; i < 26; i++) {
            if (record[i] != 0) return false;
        }
        return true;
    }
};

Hash Map (Simpler)

class Solution {
public:
    bool isAnagram(string s, string t) {
        unordered_map<char, int> hash_s, hash_t;
        for (auto c : s) hash_s[c]++;
        for (auto c : t) hash_t[c]++;
        // unordered_map supports == operator
        return hash_s == hash_t;
    }
};

Time complexity: \(O(n)\)