402. Remove K Digits
Given a non-negative integer num represented as a string, remove k digits from the number so that the new number is the smallest possible.
Note:
- The length of num is less than 10002 and will be ≥ k.
- The given num does not contain any leading zero.
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.
Solution: Stack
class Solution(object):
def removeKdigits(self, num, k):
"""
:type num: str
:type k: int
:rtype: str
"""
stack = []
for digit in num:
while k > 0 and stack and digit < stack[-1]:
stack.pop()
k -= 1
if digit > '0' or stack:
stack.append(digit)
while k > 0 and stack:
stack.pop()
k -= 1
return ''.join(stack) or '0'