[LintCode] Two Strings Are Anagrams

Write a method anagram(s,t) to decide if two strings are anagrams or not.

Clarification

What is Anagram?
- Two strings are anagram if they can be the same after change the order of characters.

Example

Given s = "abcd", t = "dcab", return true.
Given s = "ab", t = "ab", return true.
Given s = "ab", t = "ac", return false.

Challenge 

O(n) time, O(1) extra space

Solution: 

This problem is very simple with hash maps. Store all characters and their frequencies from s, then check if t has exactly the same character set with 

the same frequencies for each character.

public class Solution {
    public boolean anagram(String s, String t) {
        if(s == null || t == null || s.length() != s.length()){
            return false;
        }
        int[] chars = new int[256];
        for(int i = 0; i < s.length(); i++){
            chars[s.charAt(i)]++;
        }
        for(int i = 0; i < t.length(); i++){
            if(chars[t.charAt(i)] == 0){
                return false;
            }
            else{
                chars[t.charAt(i)]--;
            }
        }
        return true;
    }
}