LeetCode 387. First Unique Character in a String

題目:

給定一個string，找到string中第一個非重複的index是多少，都是重複的話回傳-1。

Example 1:

Input: s = "leetcode"
Output: 0

Example 2:

Input: s = "loveleetcode"
Output: 2

Example 3:

Input: s = "aabb"
Output: -1

思路:

1. from collections import Counter (用來幫忙數字母出現次數)
2. 建立一個lookup 可以知道每一個字母出現的次數
   lookup = Counter(s)
   *如果不用到Counter的話 做法如下
   lookup = dict()
   for i in s :
   if i in lookup:
   lookup[i] +=1
   else:
   lookup[i] =1
3. for i, c enumerate(s): for 循環go through 整個詞，i是index c是字母本身
   if lookup[c] == 1:
   return i
4. 其他情況return -1

Coding:

class Solution:
    def firstUniqChar(self, s: str) -> int:
        lookup = dict()
        for i in s:
            if i in lookup:
                lookup[i] +=1
            else:
                lookup[i]=1
        
        for i, c in enumerate(s):
            if lookup[c] ==1:
                return i 
        return -1