Problem: First Unique Character in a String

Posted by Marcy on February 18, 2015

Question

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.

Solution

TODO

Code

class Solution {
    public int firstUniqChar(String s) {
        Map<Character, Integer> map = new HashMap<>();
        for(int i=0; i<s.length(); i++) {
            char c = s.charAt(i);
            map.put(c, map.getOrDefault(c, 0) + 1);
        }

        for(int i=0; i<s.length(); i++) {
            if(map.get(s.charAt(i)) == 1) return i;
        }

        return -1;
    }
}

Performance

O(n)