387. First Unique Character in a String [easy] (Python)

题目链接

https://leetcode.com/problems/first-unique-character-in-a-string/

题目原文

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.

Note: You may assume the string contain only lowercase letters.

题目翻译

给定一个字符串，找出其中第一个不重复出现的字符，返回其位置索引。如果不存在，则返回-1。
注意：假定字符串中只包含小写字母。

思路方法

思路一

先将所有字符出现的次数统计出来，再重新遍历原字符串中的字符，直到发现一个字符只出现一次，返回其下标。下面的代码用字典统计。

代码

class Solution(object):
    def firstUniqChar(self, s):
        """
        :type s: str
        :rtype: int
        """
        letters = {}
        for c in s:
            letters[c] = letters[c] + 1 if c in letters else 1
        for i in xrange(len(s)):
            if letters[s[i]] == 1:
                return i
        return -1

思路二

同思路一，用数组统计字符出现次数。

代码

class Solution(object):
    def firstUniqChar(self, s):
        """
        :type s: str
        :rtype: int
        """
        letters = [0] * 26
        for c in s:
            letters[ord(c) - 97] += 1
        for i in xrange(len(s)):
            if letters[ord(s[i]) - 97] == 1:
                return i
        return -1