【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
;
}
};