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Tested Python solution for LeetCode 402 with 22 pytest cases. Generate a practice environment with lcpy.
lcpy gen -n 402 # by problem number
lcpy gen -s remove_k_digits # by problem name
num, and an integer k, return the smallest possible integer after removing k digits from num.
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.
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.
Input: num = "10", k = 2
Output: "0"
Explanation: Remove all the digits from the number and it is left with nothing which is 0.
1 <= k <= num.length <= 10^5num consists of only digits.num does not have any leading zeros except for the zero itself.class Solution:
# Time: O(n)
# Space: O(n)
def remove_k_digits(self, num: str, k: int) -> str:
stack: list[str] = []
for digit in num:
while k and stack and stack[-1] > digit:
stack.pop()
k -= 1
stack.append(digit)
if k:
stack = stack[:-k]
return "".join(stack).lstrip("0") or "0"
| Time | Space |
|---|---|
| O(n) | O(n) |