【LeetCode & 劍指offer 刷題筆記】目錄（持續更新中...）

387. First Unique Character in a String

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.   //O(n), 以空間來換時間 class Solution { public :     int firstUniqChar ( string s )     {        unordered_map < char , int > m ; //也可直接用一個數組        for ( auto & c : s ) //基於範圍的for迴圈         {             m [ c ]++;         } //若用陣列來做統計表，由於是定長的（對普通字元，256長度），可以看做空間複雜度為O(1)        /* for(int i = 0;i<s.size();i++)         {             m[s[i]]++;         }*/                for ( int i = 0 ; i < s . size (); i ++)         {             if ( m [ s [ i ]]== 1 ) return i ;         }                return - 1 ;     } };