class Solution {

public:

    /**

     *@param A: A positive integer which has N digits, A is a string.

     *@param k: Remove k digits.

     *@return: A string

     */

    string DeleteDigits(string A, int k)

    {

        size_t n = A.size();

        int cnt = ;

        int i = ;

        while(i < n - )

        {

            if(A[i] > A[i + ])

            {

                A.erase(i, );

                if(i > ) i--;

                n --;

                if(++cnt == k)    break;

            }

            else

            {

                i ++;

            }

        }

        if(cnt < k) // all ascending, remove last

        {

            n = A.size();

            A = A.substr(, n - (k - cnt));

        }

        //  Remove leading 0s

        i = , n = A.size();

        while(i < n && A[i] == '') i ++;

        A = A.substr(i);

        if(A.empty()) A = "";

        return A;

    }

};