LeetCode知识点总结 - 387

387. First Unique Character in a String

考点	难度
Hash Table	Easy

题目

Given a string s, find the first non-repeating character in it and return its index. If it does not exist, return -1.

思路

和之前的题解法差不多。先对s里的每个字母计数，再从头到尾找出来出现次数是1的字母。

答案

public int firstUniqChar(String s) {
        HashMap<Character, Integer> counts = new HashMap<Character, Integer>();
        int len = s.length();
        for (int i = 0; i < len; i++){
            char c = s.charAt(i);
            counts.put(c, counts.getOrDefault(c, 0) + 1);
        }
        
        for (int i = 0; i < len; i++){
            if (counts.get(s.charAt(i)) == 1) return i;
        }
        return -1;
    }