Java 代码

class Solution {
    public String replaceSpaces(StringBuffer str) 
    {
        while (true)
        {
            int index = str.indexOf(" ");
            if (index == -1)
            {
               break; 
            }
            else
            {
                str.replace(index, index+1, "%20");
            }
        }
        return str.toString();
    }
}