LeetCode 387 First Unique Character in a String

LeetCode

Given a string s, find the first non-repeating character in it and return its index. If it does not exist, return -1.

Example 1:

Input: s = “leetcode”
Output: 0

Example 2:

Input: s = “loveleetcode”
Output: 2

Example 3:

Input: s = “aabb”
Output: -1

Constraints:

1 <= s.length <= 10<sup>5</sup> s consists of only lowercase English letters.

题目大意：

求字符串中第一个唯一的字符下标

解题思路：

Easy题。先统计频率，然后再遍历一次字符串找到频率为1的字符

解题步骤：

N/A

注意事项：

1. Python代码：

   def firstUniqChar(self, s: str) -> int:
   	char_to_count = collections.Counter(s)
   	for i in range(len(s)):
   		if char_to_count[s[i]] == 1:
   			return i
   	return -1

算法分析：

时间复杂度为O(n)，空间复杂度O(1), 26个字母为常量空间