#include <iostream>
#include <string>
using namespace std;
class Solution {
public:
    string replaceSpace(string s) {
        int count = 0;
        int lenth = s.size();
        for(auto i = 0; i < lenth; ++i){
            if(s[i] == ' '){
                count = count + 1;
            }
        }        
        s.resize(s.size() + 2 * count);
        for(int i = lenth - 1, j = s.size() - 1; i < j; --i, --j){
            if (s[i] != ' ')
                s[j] = s[i];
            else {
                s[j - 2] = '%';
                s[j - 1] = '2';
                s[j] = '0';
                j -= 2;
            }
        }
        return s;
    }
};

int main(){
    string s = "We are happy.";
    Solution test;
    cout<<test.replaceSpace(s)<<endl;
}