310. Remove K Digits to Create Smallest Possible Number

Remove K Digits to Create Smallest Possible Number

Given a non-negative integer num represented as a string, remove exactly k digits while keeping the remaining digits in their original order. Return the smallest possible number.

Method Signature

String removeKdigits(String num, int k)

num is the non-negative integer represented as a string.
k is the exact number of digits to remove.
Return the smallest number that can be formed after the removals.

Output Rules

The relative order of the remaining digits must not change.
Remove all leading zeroes from the result.
Return "0" if every digit is removed or the remaining digits represent zero.

Constraints

1 ≤ num.length() ≤ 10,001
0 ≤ k ≤ num.length()
num contains only digits from '0' to '9'.
num has no leading zeroes unless num is "0".

Examples

Example 1

removeKdigits(num = "7650281", k = 3)

Output: "281"

Removing 7, 6, and 5 produces the smallest possible result.

Example 2

removeKdigits(num = "10045", k = 1)

Output: "45"

Removing 1 leaves "0045", whose leading zeroes are removed.

Example 3

removeKdigits(num = "9876", k = 2)

Output: "76"

Removing the first two digits gives the smallest possible remaining number.

Example 4

removeKdigits(num = "5000", k = 2)

Output: "0"

The smallest remaining value consists only of zeroes, so the result is normalized to "0".