[LeetCode] First Unique Character in a String 字符串第一個不同字符

 

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.

 

這道題確實沒有什么難度，我們只要用哈希表建立每個字符和其出現次數的映射，然后按順序遍歷字符串，找到第一個出現次數為1的字符，返回其位置即可，參見代碼如下：

 

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;
    }
};

 

類似題目：

Sort Characters By Frequency

 

參考資料：

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

 

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