Reverse Words in a String

Source

• lintcode: Reverse Words in a String

Given an input string, reverse the string word by word.

For example,
Given s = "the sky is blue",
return "blue is sky the".

Clarification
What constitutes a word?
A sequence of non-space characters constitutes a word.
Could the input string contain leading or trailing spaces?
Yes. However, your reversed string should not contain leading or trailing spaces.
How about multiple spaces between two words?
Reduce them to a single space in the reversed string.

Python

class Solution:
    # @param s : A string
    # @return : A string
    def reverseWords(self, s):
        if s is None:
            return None

        last=len(s)-1
        result = []

        while last>=0:
            tmp=[]
            while s[last]!=' ':
                tmp.append(s[last])
                last-=1
                if last<0:
                    break
            else:
                last-=1

            if tmp:
                if result:
                    result.append(' ')
                self.reverse(tmp, 0, len(tmp)-1)
                result.append(''.join(tmp))
        return ''.join(result)

    def reverse(self, s, left, right):
        while left<right:
            tmp = s[left]
            s[left] = s[right]
            s[right] = tmp
            left+=1
            right-=1

Java

public class Solution {
    /**
     * @param s : A string
     * @return : A string
     */
    public String reverseWords(String s) {
        StringBuilder result = new StringBuilder();
        int last=s.length()-1;

        while(last>=0){
            StringBuilder tmp = new StringBuilder();

            while(s.charAt(last)!=' '){
                //tmp.append(s.charAt(last));
                tmp.insert(0, s.charAt(last));
                last--;
                if(last<0) break;
            }
            last--;
            if(tmp.length()>0){
                if(result.length()>0){
                    result.append(" ");
                }
                //reverse(tmp, 0, tmp.length()-1);
                result.append(tmp.toString());
            }
        }
        return result.toString();
    }

    // public void reverse(StringBuilder sb, int left, int right){
    //     while(left<right){
    //         char c = sb.charAt(left);
    //         sb.setCharAt(left, sb.charAt(right));
    //         sb.setCharAt(right, c);
    //         left++;
    //         right--;
    //     }

    // }
}