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.

这里需要注意用hashmap时不能说他没containskey就返回，因为他加的数可能是s里面有的。所以用int[26]统计各个字母出现的次数比较靠谱。

public class Solution {
    public char findTheDifference(String s, String t) {
        int[] chars = new int[26];
        char result = 0;
        for (int i = 0; i < s.length(); i++) {
            chars[s.charAt(i) - 'a']++;
            chars[t.charAt(i) - 'a']--;
        }
        chars[t.charAt(t.length() - 1) - 'a']--;
        for (char j = 0; j < 26; j ++) {
            if (chars[j] != 0) {
                result = (char)(j + 'a');
                break;
            }
        }
        return result;
    }
}

或者用 Bit manipulation的异或操作。

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