Smallest Number After Removing K Digits

Problem

Remove exactly k digits from the decimal string num to produce the smallest possible number, and return it without leading zeros.

Maintain a monotonic increasing stack: pop larger digits while removals remain and the new digit is smaller. After the scan, drop digits from the end if removals remain, strip leading zeros, and return 0 for an all-zero result.

Hint

A bigger digit earlier is always worse, so pop it whenever a smaller digit can replace it.

Test cases

case 1

in: ["1432219",3]

expected: "1219"

case 2

in: ["10200",1]

expected: "200"

case 3

in: ["10",2]

expected: "0"

case 4

in: ["9",1]

expected: "0"

case 5

in: ["112",1]

expected: "11"

Starter codePython

def remove_k_digits(num, k):
    # Your code here
    pass

5 test cases · run your code against them in the editor