387. First Unique Character in a String

This is very similar to the second question I was asked in an Amazon interview back to 2014. Here's my solution for it.

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.

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public class Solution { public int firstUniqChar(String s) { if(s==null ||s.length()==0)return -1; if(s.length()==1)return 0; int[] positions = new int[26]; for(int i=0;i<26;i++){ positions[i]=Integer.MIN_VALUE; } //set repeated ones with -1 for(int i=0;i<s.length();i++){ int curCharIndex = s.charAt(i)-'a'; if(positions[curCharIndex]==Integer.MIN_VALUE){ positions[curCharIndex]=i; }else if(positions[curCharIndex]>=0){ positions[curCharIndex]=-1; } } for(int i=0;i<s.length();i++){ int curCharIndex = s.charAt(i)-'a'; if(positions[curCharIndex]>=0){ return positions[curCharIndex]; } } return -1; } }