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.
思路：扫一遍，用array记录char的重复次数。扫第二遍，碰到第一个char的个数是1就输出，扫完没有就是－1.
public class Solution {public int firstUniqChar(String s) {if(s.length()==0){return -1;}int[] res=new int[128];for(int i=0;i<s.length();i++){if(res[s.charAt(i)]==0){res[s.charAt(i)]=1;}else{res[s.charAt(i)]++;}}for(int i=0;i<s.length();i++){if(res[s.charAt(i)]==1){return i;}}return -1;} }
)
)
