#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.

class Solution(object):
	def removeKdigits(self, num, k):
		"""
		:type num: str
		:type k: int
		:rtype: str
		"""
		ans=[]
		for i in num:
			while ans and k and ans[-1]>i:
				ans.pop()
				k-=1
			ans.append(i)
		return ''.join(ans).lstrip('0')[:-k or None] or '0'