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.

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public class Solution {    public int firstUniqChar(String s) {        if (s == null) {            return -1;        }        int length = s.length();        if (length < 2) {            return length -1;        }                char[] array = s.toCharArray();        for (int i = 0; i < length; i++) {            boolean b = true;            if (array [i] == '0') {                    continue;                }            for (int j = i + 1; j < length; j++) {                                if (array[i] == array[j]) {                    b = false;                    array[j] = '0';                }            }            if (b) {                return i;            }        }        return -1;    }}