# # 【LeetCode】402. Remove K Digits 解题报告（Python）

## # 题目描述：

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.
``````

## # 解题方法

``````class Solution(object):
def removeKdigits(self, num, k):
"""
:type num: str
:type k: int
:rtype: str
"""
if len(num) == k:
return '0'
stack = []
for n in num:
while stack and k and int(stack[-1]) > int(n):
stack.pop()
k -= 1
stack.append(n)
while k:
stack.pop()
k -= 1
if not stack:
return '0'
return str(int("".join(stack)))
``````

## # 日期

2018 年 7 月 13 日 ———— 早起困一上午，中午必须好好休息才行啊