【两次过】Lintcode 1282. Reverse Vowels of a String

Write a function that takes a string as input and reverse only the vowels of a string.

样例

Example 1:
Given s = "hello", return "holle".

Example 2:
Given s = "lintcode", return "lentcodi".

解题思路：

    对撞指针。使用哈希表存储元音字母，注意大写也算！指针i，j分别指向左边的元音字母与右边的元音字母。

class Solution {
public:
    /**
     * @param s: a string
     * @return: reverse only the vowels of a string
     */
    string reverseVowels(string &s) 
    {
        // write your code here
        int i = 0;
        int j = s.size()-1;
        unordered_set<char> vowels{'a','e','i','o','u','A','E','I','O','U'};
        
        string res = s;
        while(i<j)
        {
            if(vowels.count(res[i])&&vowels.count(res[j]))
                swap(res[i++],res[j--]);
            else if(vowels.count(res[i])==0)
                i++;
            if(vowels.count(res[j])==0)
                j--;
        }
        
        return res;
    }
};