LeetCode 345 - Reverse Vowels of a String

http://blog.csdn.net/ebowtang/article/details/51228095

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".

https://leetcode.com/discuss/98987/java-standard-two-pointer-solution

In the inner while loop, don't forget the condition "start less than end" while incrementing start and decrementing end. This is my friend's google phone interview question. Cheers! // update! May use a HashSet to reduce the look up time to O(1)

public String reverseVowels(String s) {
    if(s == null || s.length()==0) return s;
    String vowels = "aeiouAEIOU";
    char[] chars = s.toCharArray();
    int start = 0;
    int end = s.length()-1;
    while(start<end){

        while(start<end && !vowels.contains(chars[start]+"")){
            start++;
        }

        while(start<end && !vowels.contains(chars[end]+"")){
            end--;
        }

        char temp = chars[start];
        chars[start] = chars[end];
        chars[end] = temp;

        start++;
        end--;
    }
    return new String(chars);
}

http://www.programcreek.com/2015/04/leetcode-reverse-vowels-of-a-string-java/

Use hashset

public String reverseVowels(String s) { ArrayList<Character> vowList = new ArrayList<Character>(); vowList.add('a'); vowList.add('e'); vowList.add('i'); vowList.add('o'); vowList.add('u'); vowList.add('A'); vowList.add('E'); vowList.add('I'); vowList.add('O'); vowList.add('U');   char[] arr = s.toCharArray();   int i=0; int j=s.length()-1;   while(i<j){ if(!vowList.contains(arr[i])){ i++; continue; }   if(!vowList.contains(arr[j])){ j--; continue; }   char t = arr[i]; arr[i]=arr[j]; arr[j]=t;   i++; j--; }   return new String(arr); }

https://leetcode.com/discuss/99000/4ms-java-assume-ascii-input
private final char[] vowels = new char[]{'a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'}; public String reverseVowels(String s) { boolean[] map = new boolean[256]; for (char c : vowels) map[c] = true; int i = 0; int j = s.length() - 1; char[] word = s.toCharArray(); while (i < j) { while (i < j && !map[word[i]]) i++; while (i < j && !map[word[j]]) j--; char temp = word[i]; word[i] = word[j]; word[j] = temp; i++; j--; } return new String(word); }

典型的双指针问题，注意边界条件即可！

    void swapchar(string &str,int pos1,int pos2)  
    {  
        char tmpch=str[pos2];  
        str[pos2]=str[pos1];  
        str[pos1]=tmpch;  
    }  
    string reverseVowels(string s) {
        char base[10]={'a','e','i','o','u','A','E','I','O','U'};
        set<char> seting(base,base+10);
        int startpos=0,endpos=s.size()-1;
        while(startpos < endpos )
        {
            while( startpos < endpos && seting.find(s[startpos]) == seting.end())
                startpos++;
            while( startpos < endpos && seting.find(s[endpos]) == seting.end())
                endpos--;
            if(startpos < endpos)    
                swapchar(s,startpos++,endpos--);    
        }
        return s;
    }