387 First Unique Character in a String 字符串中的第一个唯一字符
Description:
Given a string, find the first non-repeating character in it and return it's index. If it doesn't exist, return -1.
Example :
s = "leetcode"
return 0.
s = "loveleetcode",
return 2.
Note:
You may assume the string contain only lowercase letters.
题目描述:
给定一个字符串，找到它的第一个不重复的字符，并返回它的索引。如果不存在，则返回 -1。
示例 :
s = "leetcode"
返回 0.
s = "loveleetcode",
返回 2.
注意：
您可以假定该字符串只包含小写字母。
思路:
可以建立一个 26位的数组用来记录 s中出现的字符及次数, 再遍历一次记录第一个出现的 1即可
时间复杂度O(n), 空间复杂度O(1)
代码:
C++:
class Solution
{
public:
int firstUniqChar(string s)
{
int count[26] = {0};
for (int i = 0; i < s.size(); i++) ++count[s[i] - 'a'];
for (int i = 0; i < s.size(); i++) if(count[s[i] - 'a'] == 1) return i;
return -1;
}
};
Java:
class Solution {
public int firstUniqChar(String s) {
int count[] = new int[26];
for (int i = 0; i < s.length(); i++) count[s.charAt(i) - 'a']++;
for (int i = 0; i < s.length(); i++) if(count[s.charAt(i) - 'a'] == 1) return i;
return -1;
}
}
Python:
class Solution:
def firstUniqChar(self, s: str) -> int:
return [s.index(i) for i in s if s.find(i) == s.rfind(i)][0] if [s.index(i) for i in s if s.find(i) == s.rfind(i)] else -1
