[LeetCode] 387. First Unique Character in a String

Given a string, find the first non-repeating character in it and return its index. If it doesn't exist, return -1.

Examples:

s = "leetcode"
return 0.

s = "loveleetcode"
return 2.

Note: You may assume the string contains only lowercase English letters.

第一个独一无二的字符。题意是给一个字符串，请输出第一个出现的独一无二的字符，或者说请输出第一个出现的在整个字符串里面只出现过一次的字符。

还是counting sort的思路。对input数组扫描两次。第一次需要用hashmap记录所有字符出现的次数，第二次需要找到的是只出现过一次的字符。

时间O(n)

空间O(n)

Java实现

class Solution {
    public int firstUniqChar(String s) {
        int[] count = new int[26];
        for (int i = 0; i < s.length(); i++) {
            count[s.charAt(i) - 'a']++;
        }
        for (int j = 0; j < s.length(); j++) {
            if (count[s.charAt(j) - 'a'] == 1) {
                return j;
            }
        }
        return -1;
    }
}

JavaScript实现

/**
 * @param {string} s
 * @return {number}
 */
var firstUniqChar = function(s) {
    let map = {};
    for (let i = 0; i < s.length; i++) {
        let cur = s.charAt(i);
        if (!map[cur]) {
            map[cur] = 1;
        } else {
            map[cur]++;
        }
    }

    for (let j = 0; j < s.length; j++) {
        let cur = s.charAt(j);
        if (map[cur] === 1) {
            return j;
        }
    }
    return -1;
};

LeetCode 题目总结