The first character of leetcode sword offer that only appears once (12)

Title Description

character string s Find the first character that appears only once . without , Return a single space . s Contains only lowercase letters .

Example 1:

 Input ：s = "abaccdeff"
 Output ：'b'

Example 2:

 Input ：s = "" 
 Output ：' '

python3 Realization

Coding ideas ： Slicing method (python alone possess ), It can also be used. hash map

class Solution:
    def firstUniqChar(self, s: str) -> str:
        rs = " "
        for i in range(len(s)):
            if s[i] not in s[:i] and s[i] not in s[i+1:]:
                return s[i]
        return rs

c++ Realization

Encoding idea ： Storage frequency using hash table

class Solution {
public:
    char firstUniqChar(string s) {
        unordered_map<int, int> freq;
        for(char c:s){
            ++freq[c];
        }
        for(int i=0; i<s.size();i++){
            if(freq[s[i]] == 1)
                return s[i];
        }
        return ' ';

    }
};