<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 s, int k) {
        if(int(s.size())<=k)return "0";
         stack<int >s1;
        // map<char,int>m;
//         for(int i=0;i<s.size();i++){
//             if(m.find(s[i])==m.end()){
//                 m[s[i]]=1;
//             }
//             else{
//               m[s[i]]++;

//             }
//         }
        for(int i=0;i<s.size();i++){
            while(!s1.empty()&&s1.top()>s[i]-0&&k!=0){
                 // v[s1.top()-'a']=0;
                 s1.pop();
                k--;
                
            }
             s1.push(s[i]-0);
          
        }
        
        string ans="";
        while(!s1.empty()){
            if(s1.top()==0&&ans==""){
                continue;
            }
            else{
               
                ans+=s1.top();
                s1.pop();
            }
        }
        if(k!=0)
        {
            ans=ans.substr(k);
        }
        reverse(ans.begin(), ans.end());
        int j=0;
            string sa="";
        for(auto i:ans){
            if(j==0&&i=='0'){
                continue;
            }
            else{
                sa+=i;
                j++;
            }
            
        }
        return sa!=""?sa:"0";
        
    }
};
12600