389. Find the Difference

Given two strings s and t which consist of only lowercase letters.

String t is generated by random shuffling string s and then add one more letter at a random position.

Find the letter that was added in t.

Example:

Input:
s = "abcd"
t = "abcde"

Output:
e

Explanation:
'e' is the letter that was added.

一刷
题解：
方法一：词频统计

class Solution {
    public char findTheDifference(String s, String t) {
        int[] freq = new int[26];
        for(int i=0; i<s.length(); i++){
            freq[s.charAt(i) - 'a']++;
        }
        for(int i=0; i<t.length(); i++){
            freq[t.charAt(i) - 'a']--;
            if(freq[t.charAt(i) - 'a']<0) return t.charAt(i);
        }
        return 'a';
    }
}

方法二： XOR

public char findTheDifference(String s, String t) {
    int n = t.length();
    char c = t.charAt(n - 1);
    for (int i = 0; i < n - 1; ++i) {
        c ^= s.charAt(i);
        c ^= t.charAt(i);
    }
    return c;
}