First Unique Character in a String
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https://leetcode.com/problems/first-unique-character-in-a-string/#/description
题目思路:
题目的要求是让我们在一个字符串中找到第一个没有重复的字符并返回它的索引。首先这个字符串不重复的字符有多个,且重复的字符重复次数不是偶数,所以不能通过异或全部字符来求解。但是题目的提示中说可以假设所有的字符都是小写字母,所以很容易想到直接用个数组来表示26个小写字母。(a强制转化为int类型,值为97,后按字母表顺序依次增加1)先遍历一遍字符串,每次遇到某个字母,则其对应的数组位置的值+1。所有出现过一遍的字母,则对应的数组位置的值为1。然后再遍历一遍字符串,如果找出第一个对应数组位置值为1的字母索引并返回,如果找不到,返回-1。
public class Solution { public int firstUniqChar(String s) { int[] flag = new int[26]; if(s.length() <= 0) { return -1; } for (int i = 0; i < s.length(); i++) { flag[(int)s.charAt(i)-97]++; } for(int i = 0; i < s.length(); i++) { if(flag[(int)s.charAt(i)-97] == 1) return i; } return -1; }}
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