First Unique Character in a String

Question

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.

Tags

• String
• Hashmap

Thought

Here, we can two sets to record the duplicated and unique characters in the string.

• dupSet: Store the duplicated characters
• firstSet: Store the unique characters

Code

class Solution(object):
    def firstUniqChar(self, s):
        """
        :type s: str
        :rtype: int
        """
        dupSet = set()
        firstSet = set()
        for ch in s:
            if ch in dupSet:
                continue
            if ch in firstSet:
                firstSet.remove(ch)
                dupSet.add(ch)
            else:
                firstSet.add(ch)
        for i, ch in enumerate(s):
            if ch in firstSet:
                return i
        return -1