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"

Runtime: 13ms.

 1 class Solution {
 2 public:
 3     /**
 4      *@param A: A positive integer which has N digits, A is a string.
 5      *@param k: Remove k digits.
 6      *@return: A string
 7      */
 8     string DeleteDigits(string A, int k) {
 9         // wirte your code here
10         
11         // find the first decrease index and erase index - 1
12         // continue with the new string
13         if (k == A.size()) return "";
14         
15         int count = 0;
16         while (count++ < k) {
17             bool erased = false;
18             for (int i = 1; i < A.size(); i++) {
19                 if (A[i] < A[i - 1]) {
20                     A.erase(i - 1, 1);
21                     erased = true;
22                     break;
23                 }
24             }
25             if (!erased) A.erase(A.size() - 1, 1);
26         }
27         // ensure that there is no leading 0s in A
28         int i = 0;
29         while (i < A.size() && A[i] == '0') i++;
30         return A.substr(i, A.size() - i);
31     }
32 };