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.

public class Solution {
    public int firstUniqChar(String s) {
        // Can cover this situation, code below is not needed.
        // if (s == null || s.length() == 0) {
        //     return -1;
        // }
        /** Solution 1:
        for (int i = 0; i < s.length(); i++) {
            if (s.lastIndexOf(s.charAt(i)) == s.indexOf(s.charAt(i))) {
                return i;
            }
        }
        return -1;
        */
        //Solution 2:
        int[] map = new int[26];
        for (int i = 0; i < s.length(); i++) {
            map[s.charAt(i) - 'a'] += 1;
        }
        for (int j = 0; j < s.length(); j++) {
            if (map[s.charAt(j) - 'a'] == 1) {
                return j;
            }
        }
        return -1;
    }
}
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