Q2:Reverse Words in a String

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.

MyAnswer 1 (Java):

public class Solution {
    public String reverseWords(String s) {
        String result = "";
        int i = 0;
        int j = s.length();
        for(i = s.length()-1; i >= 0; i--)
        {
            if(s.charAt(i) == ' ')
            {
                if(i == s.length()-1)
                {
                    j = i;
                    //continue;
                }
                else if(i == 0)
                {
                    //i++;
                    break;
                }
                else if(j == i+1)
                {
                    j = i;
                    //continue;
                }
                else
                {
                    result = result.concat(s.substring(i+1,j)+" ");
                    j = i;
                }
            }
        }
        result = result.concat(s.substring(i+1,j));
        if(!result.isEmpty() && result.charAt(result.length()-1) == ' ')
            result = result.substring(0,result.length()-1);
        return result;
    }
}

 使代码更加精简，改为：

MyAnswer 2(Java):

public class Solution {
    public String reverseWords(String s) {
        
        String result = "";
        int j = s.length();
        int i = j-1;
        
        for(; i >= 0; i--)
        {
            if(s.charAt(i) == ' ')
            {
                if(i == 0)
                {
                    break;
                }
                else if(i != s.length()-1 && j != i+1)
                {
                    result = result.concat(s.substring(i+1,j)+" ");
                }
                j = i;
            }
        }
        
        result = result.concat(s.substring(i+1,j));
        
        int k = result.length();
        if(!result.isEmpty() && result.charAt(k-1) == ' ')
            result = result.substring(0,k-1);
        return result;
    }
}

MyAnswer3 (C++):

class Solution {
public:
    void reverseWords(string &s) {
        string result = "";
        int j = 0;
        int i;
        for(i = s.length()-1; i >= 0; i--)
        {
            if(s[i] == ' ')
            {
                if(j == 0)
                    continue;
                result = result + s.substr(i+1, j) + " ";
                j = 0;
                continue;
            }
            j++;
        }
        result = result + s.substr(i+1, j);
        s = (result[result.length()-1] == ' ')?result.substr(0,result.length()-1):result;
    }
};