## 402. Remove K Digits

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 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.

Constraints:

`1 <= k <= num.length <= 105`

`num`

consists of only digits.`num`

does not have any leading zeros except for the zero itself.

Solution:

We need to make the smallest number by removing K digits. So we will remove the digits that are largest from the left.

Ex- if the num is "654" and k is 1 then we will remove 6

Ex- if the num is "654" and k is 1 then we will remove 6

if the num is "456" and k is 1 then we will remove 6

We will keep a stack and whenever the current digit is smaller than the top of the stack we will pop the stack until k>0 and the stack is not empty and the current digit is smaller than the top.

Another condition is that the current digit is 0 and the size of the stack is 1 and only contains 0 so we need to pop it.

If we have iterated over num and still k>0 then we need to pop the stack until k>0.

Now we can get our answer easily.

Now we can get our answer easily.

See the code below for better understanding.

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