<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 {
public:
    string removeKdigits(string num, int k) {
        // string smallInt;

        // smallInt.push_back(num[0]);
        // for(int i=1;i<num.size();i++){
        //     if(num[i-1]>num[i] && k>0){
        //         smallInt.pop_back();
        //         k--;
        //     }
        //     if(smallInt.length() > 0 || num[i] != '0') {
        //         smallInt.push_back(num[i]);
        //     }
        // }

        // while(smallInt.length() > 0 && k > 0) {
        //     smallInt.pop_back();
        //     k--;
        // }

        // if(smallInt == "") {
        //     return "0";
        // }

        // return smallInt;

        string result = "";
        int n = num.length();
        
        for(int i = 0; i < n; i++) {
            while(result.length() > 0 && result.back() > num[i] && k > 0) {
                result.pop_back();
                k--;
            }
            
            if(result.length() > 0 || num[i] != '0') {
                result.push_back(num[i]);
            }
        }
        
        while(result.length() > 0 && k > 0) {
            result.pop_back();
            k--;
        }

        if(result == "") {
            return "0";
        }
        
        return result;
    }
};

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