Reverse Vowels of a String

07/18/2016 String Two Pointers

Question
Solution

Question

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

Example 1:

Given s = "hello", return "holle".

Example 2:

Given s = "leetcode", return "leotcede".

Solution

Result: Accepted Time: 4 ms

Here should be some explanations.

static bool is_vowels[256]={0};
static bool is_init = false;
char vowels[]="euioaEUIOA";

char* reverseVowels(char* s) {
    if(!is_init)
    {
        is_init = true;
        for(int i = 0; vowels[i]!='\0';i++)
            is_vowels[vowels[i]] = true;
    }
    int low = 0;
    int up = strlen(s);
    char tmp;
    while(low < up)
    {
        while(low < up && !is_vowels[s[low]])
            low ++;
        while(low < up && !is_vowels[s[up]])
            up --;
        if(low < up)
        {
            tmp = s[low];
            s[low++] = s[up];
            s[up--] = tmp;
        }
    }
    
    return s;
}

Complexity Analytics

Time Complexity: $O(n)$
Space Complexity: $O(1)$