LeetCode 387 First Unique Character in a String

LeetCode

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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:

<pre>Input: s = "leetcode" Output: 0 </pre>

Example 2:

<pre>Input: s = "loveleetcode" Output: 2 </pre>

Example 3:

<pre>Input: s = "aabb" Output: -1 </pre>

Constraints:

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

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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：

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