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class Replacement {
public:
    string replaceSpace(string iniString, int length) {
        // count zeros
        int last = length + 2 * count(iniString.begin(), iniString.begin()+length, ' ');
        iniString.resize(last);
        // reverse filling
        for (int i = length-1, j = last-1; i >= 0; --i) {
            if (iniString[i] != ' ') iniString[j--] = iniString[i];
            else {
                iniString.replace(j-2, 3, "%20");
                j -= 3;
            }
        }
        return iniString;
    }
};