All problems

Remove K Digits

Medium · stack

You are given num, a string of digits that writes a non-negative whole number, and an integer k. Delete exactly k digits from num. The digits that are left keep their original order.

Return the smallest number you can make this way, as a string. The answer must not have leading zeros: if zeros end up at the front, drop them. If no digits are left, or only zeros are left, return "0".

Examples

Example 1

Input: num = "4132", k = 2

Output: "12"

Deleting the 4 and the 3 leaves 12, and no other choice of two digits gives a smaller number.

Example 2

Input: num = "10200", k = 1

Output: "200"

Deleting the 1 leaves 0200, and the leading zero is dropped.

Example 3

Input: num = "9", k = 1

Output: "0"

Nothing is left, so the answer is 0.

Constraints

• 1 <= len(num) <= 10^5
• 0 <= k <= len(num)
• num contains only the digits 0 to 9.
• num has no leading zeros, except when num is exactly "0".