class Solution {

public:
string replaceSpaces(string &str) {
    int len = str.size();
    int i = 0;
    while(i<str.size()){
        if(str[i] == ' '){

            string substr1 = str.substr(0,i);
            string substr2 = "%20";
            string substr3 = str.substr(i+1);
            str = substr1+substr2+substr3;
            i += 2; 
        }
         i+=1;
    }
    return str;
}

};