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[leetcode]first unique character in a string

admin 11月 12, 2020 0

题目描述

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

Examples:

s = "leetcode"
return 0.

s = "loveleetcode",
return 2.

Note: You may assume the string contain only lowercase letters.

解题思路和代码

首先遍历一遍字符串，用hash统计每个字符出现的次数即可，然后第二遍遍历找出第一个只出现一次的字符。

public class  {
    public int firstUniqChar(String s) {
        
        int[] freq = new int[256];

        for(char ch : s.toCharArray()){
            freq[ch]++;
        }

        for(int i = 0; i < s.length(); i++){
            if(freq[s.charAt(i)] == 1) return i;
        }

        return -1;
    }
}