class Solution 
{
public:
    string replaceSpace(string s) 
    {
		int count = 0;
		for (int i = 0; i < s.size(); ++i)//统计空格的数量
		{
			if (s[i] == ' ')
				++count;
		}

		int sOldNum = s.size();
		s.resize(sOldNum + 2 * count);//改变字符串的大小
		int sNewNum = s.size();

		for (int i = sNewNum - 1, j = sOldNum - 1; j < i; --i, --j)//从后往前赋值
		{
			if (s[j] != ' ')
			{
				s[i] = s[j];
			}
			else
			{
				s[i] = '0';
				s[i-1] = '2';
				s[i-2] = '%';
				i -= 2;
			}
		}
        
		return s;
    }
};