Remove K Digits — LeetCode 402 Python Solution

The problem

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

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.

Python solution

class Solution:
    def removeKdigits(self, num: str, k: int) -> str:
        stk = []
        remain = len(num) - k
        for c in num:
            while k and stk and stk[-1] > c:
                stk.pop()
                k -= 1
            stk.append(c)
        return ''.join(stk[:remain]).lstrip('0') or '0'

Complexity

Pattern: Stack

When the most recent unresolved thing is the one that matters, use a stack. LeetCode 402. Remove K Digits is filed here because LeetCode tags it Stack, which is the vocabulary this hub collects.

The stack guide has the Python template for the pattern and the 194 LeetCode problems that use it.

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