Difficulty:easy

 More:【目录】LeetCode Java实现

Description

https://leetcode.com/problems/first-unique-character-in-a-string/

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.

Intuition

Use HashMap( or int[256] ) to store the frequency of each character.

Solution

    public int firstUniqChar(String s) {

        int[] times = new int[26];

        for(int i=0; i<s.length(); i++)

            times[s.charAt(i)-'a']+=1;

        for(int i=0; i<s.length(); i++){

            if(times[s.charAt(i)-'a']==1)

                return i;

        }

        return -1;

    }

Complexity

Time complexity : O(n)

Space complexity : O(1)

 More:【目录】LeetCode Java实现