請實現一個函式，將一個字串中的每個空格替換成“%20”。例如，當字串為We Are Happy.則經過替換之後的字串為We%20Are%20Happy。

============Python============

# -*- coding:utf-8 -*-
class Solution:
    # s 源字串
    def replaceSpace(self, s):
        # write code here
        res = s.split(' ');
        ans = '';
        for i in range(len(res) - 1):
            ans 
 
+= res[i]
            ans += '%20'
        ans += res[-1]
        return ans

================Java==============

public class Solution {
    public String replaceSpace(StringBuffer str) {
        //遍歷一遍字串找出空格的數量
        if (str == null || str.length() < 0) {
            return null;
        }
        int spacenum 
 
= 0;  //計算空格數
        for (int i = 0; i < str.length(); i++) {
            if (str.charAt(i) == ' ')
                spacenum++;
        }
        int indexold = str.length() - 1;
        int newlength = str.length() + spacenum * 2;
        int indexnew = newlength - 1;
        str.setLength(newlength);
        
 
for (;indexold>=0 && indexold<newlength; --indexold) {
            if (str.charAt(indexold) == ' '){
                str.setCharAt(indexnew--, '0');
                str.setCharAt(indexnew--, '2');
                str.setCharAt(indexnew--, '%');
            } else {
                str.setCharAt(indexnew--, str.charAt(indexold));
            }
        }
        return str.toString();
    }
}