题解 | #第一个只出现一次的字符#

import java.util.*;

public class Solution {
    public int FirstNotRepeatingChar(String str) {

        // 一些特殊情况的处理
        if (0 == str.length()) {
            return -1;
        }
        if (1 == str.length()) {
            return 0;
        }

        HashMap<Character, Integer> hashMap = new HashMap<>();
        char[] chrs = str.toCharArray();
        for (char chr : chrs) {
            int num = hashMap.getOrDefault(chr, 0);
            num++;
            hashMap.put(chr, num);
        }
        int res = -1;
        for (int i = 0; i < chrs.length; i++) {
            char chr = chrs[i];
            int num = hashMap.get(chr);
            if (num == 1) {
                res = i;
                break;
            }
        }
        return res;
    }
}