387. First Unique Character in a String

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

Python

First Solution

• Time: O(N^2)
• Space: O(M) # M for duplicated chars count

class Solution:
    def firstUniqChar(self, s: str) -> int:
        cur = 0
        seem = set()

        while cur < len(s):
            char = s[cur]
            if char in seem:
                cur += 1
                continue

            if char not in s[cur+1:]:
                return cur

            seem.add(char)
            cur += 1
        return -1

Second Solution

• Time: O(N)
• Space: O(M)

from collections import Counter


class Solution:
    def firstUniqChar(self, s: str) -> int:
        counts = Counter(s)

        uniq_chars = [c for c, v in counts.items() if v == 1]

        if not uniq_chars:
            return -1

        return min([s.index(c) for c in uniq_chars])