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.

 

这道题确实没有什么难度,我们只要用哈希表建立每个字符和其出现次数的映射,然后按顺序遍历字符串,找到第一个出现次数为1的字符,返回其位置即可,参见代码如下:

 

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

 

类似题目:

Sort Characters By Frequency

 

参考资料:

https://leetcode.com/problems/first-unique-character-in-a-string/

https://leetcode.com/problems/first-unique-character-in-a-string/discuss/86348/Java-7-lines-solution-29ms

 

LeetCode All in One 题目讲解汇总(持续更新中…)


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