Delete Digits

Source

• lintcode: Delete Digits

Given string A representative a positive integer
which has N digits, remove any k digits of the
number, the remaining digits are arranged according
to the original order to become a new positive integer.

Find the smallest integer after remove k digits.

N <= 240 and k <= N,

Example
Given an integer A = "178542", k = 4

return a string "12"

Java

public class Solution {
    /**
     *@param A: A positive integer which has N digits, A is a string.
     *@param k: Remove k digits.
     *@return: A string
     */
    private String remove(String A, int pos) {
        return A.substring(0, pos) + A.substring(pos + 1, A.length());
    }

    public String DeleteDigits(String A, int k) {
        if (A.length() == k) {
            return "";
        }

        for (int i = 0; i < k; i++) {
            for (int j = 0; j < A.length(); j++) {
                if (j == A.length() - 1 || A.charAt(j + 1) < A.charAt(j)) {
                    A = remove(A, j);
                    break;
                }
            }
        }

        int i = 0;
        while (i < A.length() - 1 && A.charAt(i) == '0') {
            i++;
        }
        return A.substring(i, A.length());
    }
}