[LeetCode]--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.

用数组记录字符的老办法。

public char findTheDifference(String s, String t) {
        int[] count = new int[248];
        for (int i = 0; i < s.length(); i++)
            count[s.charAt(i) - 'a']++;
        for (int i = 0; i < t.length(); i++) {
            count[t.charAt(i) - 'a']--;
            if (count[t.charAt(i) - 'a'] < 0)
                return t.charAt(i);
        }
        return ' ';
    }

用两个map记录字符及字符出现的次数。

public char findTheDifference(String s, String t) {
        Map<Character, Integer> sMap = new HashMap<Character, Integer>();
        Map<Character, Integer> tMap = new HashMap<Character, Integer>();
        for (int i = 0; i < t.length(); i++) {
            if (i < s.length())
                if (!sMap.containsKey(s.charAt(i)))
                    sMap.put(s.charAt(i), 1);
                else
                    sMap.put(s.charAt(i), sMap.get(s.charAt(i)) + 1);

            if (!tMap.containsKey(t.charAt(i)))
                tMap.put(t.charAt(i), 1);
            else
                tMap.put(t.charAt(i), tMap.get(t.charAt(i)) + 1);
        }
        for (Character c : tMap.keySet()) {
            if (!sMap.containsKey(c))
                return c;
            if (sMap.containsKey(c) && tMap.get(c) > sMap.get(c))
                return c;
        }
        return ' ';
    }