<p>Given string num representing a non-negative integer <code>num</code>, and an integer <code>k</code>, return <em>the smallest possible integer after removing</em> <code>k</code> <em>digits from</em> <code>num</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> num = &quot;1432219&quot;, k = 3
<strong>Output:</strong> &quot;1219&quot;
<strong>Explanation:</strong> Remove the three digits 4, 3, and 2 to form the new number 1219 which is the smallest.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> num = &quot;10200&quot;, k = 1
<strong>Output:</strong> &quot;200&quot;
<strong>Explanation:</strong> Remove the leading 1 and the number is 200. Note that the output must not contain leading zeroes.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> num = &quot;10&quot;, k = 2
<strong>Output:</strong> &quot;0&quot;
<strong>Explanation:</strong> Remove all the digits from the number and it is left with nothing which is 0.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= k &lt;= num.length &lt;= 10<sup>5</sup></code></li>
	<li><code>num</code> consists of only digits.</li>
	<li><code>num</code> does not have any leading zeros except for the zero itself.</li>
</ul>

class Solution:
    def removeKdigits(self, num: str, k: int) -> str:
        num = [int(n) for n in num] # 1432219
        stack=[num[0]] # 1, 2, 
        removed=0 # 1, 2,3 
        i=1 # 2,3,4,5
        while stack and removed<k and i<len(num):
            if num[i]>=stack[-1]:
                stack.append(num[i])
            else:
                while stack and num[i]<stack[-1]:
                    if removed>=k:
                        break
                    stack.pop()
                    removed+=1
                stack.append(num[i])
            i+=1
        ans=0
        for n in stack:
            ans=ans*10+n
        for n in num[i:]:
            ans=ans*10+n
        ans=ans//(10)**(k-removed)

        res=""
        if ans==0:
            return "0"
        while ans!=0:
            digit=ans%10
            res=str(digit)+res
            ans=ans//10
        return res
18900