【LeetCode & 剑指offer刷题】字符串题1:50 第一个只出现一次的字符(387. First Unique Character in a String)
【LeetCode & 剑指offer 刷题笔记】目录(持续更新中...)
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), 以空间来换时间
class Solution
{
public:
int firstUniqChar(string s)
{
unordered_map<char, int> m; //也可直接用一个数组
for(auto& c:s) //基于范围的for循环
{
m[c]++;
}//若用数组来做统计表,由于是定长的(对普通字符,256长度),可以看做空间复杂度为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;
}
};