Solution: Remove K Digits

class Solution:
    def removeKdigits(self, num: str, k: int) -> str:
        
        count = 0
        stack = []

        for d in num:
            # while the number is smaller that the top of stack keep popping
            while count < k and len(stack) > 0 and int(d) < int(stack[-1]):
                stack.pop()
                count += 1

            # don't insert 0 if the stack is empty otherwise insert 
            if len(stack) == 0:
                if int(d) > 0:
                    stack.append(d)
            else:
                stack.append(d)

        # remaining number that needs to be popped out to meet k 
        while len(stack) > 0 and count < k:
            count += 1
            stack.pop()

        result = "".join(stack) 

        # empty string mean