## DEV Community

Abhishek Chaudhary

Posted on

# Remove K Digits

Given string num representing a non-negative integer `num`, and an integer `k`, return the smallest possible integer after removing `k` digits from `num`.

Example 1:

Input: num = "1432219", k = 3
Output: "1219"
Explanation: Remove the three digits 4, 3, and 2 to form the new number 1219 which is the smallest.

Example 2:

Input: num = "10200", k = 1
Output: "200"
Explanation: Remove the leading 1 and the number is 200. Note that the output must not contain leading zeroes.

Example 3:

Input: num = "10", k = 2
Output: "0"
Explanation: Remove all the digits from the number and it is left with nothing which is 0.

Constraints:

• `1 <= k <= num.length <= 105`
• `num` consists of only digits.
• `num` does not have any leading zeros except for the zero itself.

SOLUTION:

``````class Solution:
def removeKdigits(self, num: str, k: int) -> str:
n = len(num)
if n == k:
return "0"
stack = []
for i in range(n):
if len(stack) == 0:
stack.append(num[i])
else:
while len(stack) > 0 and int(num[i]) < int(stack[-1]) and len(stack) >= i - k + 1:
stack.pop()
if len(stack) == 0 or len(stack) < n - k:
stack.append(num[i])
return str(int("".join(stack)))
``````