[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 ' '; } 相关资源：python入门教程(PDF版)