<p>Given a string <code>s</code> representing a valid expression, implement a basic calculator to evaluate it, and return <em>the result of the evaluation</em>.</p>

<p><strong>Note:</strong> You are <strong>not</strong> allowed to use any built-in function which evaluates strings as mathematical expressions, such as <code>eval()</code>.</p>

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

<pre>
<strong>Input:</strong> s = &quot;1 + 1&quot;
<strong>Output:</strong> 2
</pre>

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

<pre>
<strong>Input:</strong> s = &quot; 2-1 + 2 &quot;
<strong>Output:</strong> 3
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;(1+(4+5+2)-3)+(6+8)&quot;
<strong>Output:</strong> 23
</pre>

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

<ul>
	<li><code>1 &lt;= s.length &lt;= 3 * 10<sup>5</sup></code></li>
	<li><code>s</code> consists of digits, <code>&#39;+&#39;</code>, <code>&#39;-&#39;</code>, <code>&#39;(&#39;</code>, <code>&#39;)&#39;</code>, and <code>&#39; &#39;</code>.</li>
	<li><code>s</code> represents a valid expression.</li>
	<li><code>&#39;+&#39;</code> is <strong>not</strong> used as a unary operation (i.e., <code>&quot;+1&quot;</code> and <code>&quot;+(2 + 3)&quot;</code> is invalid).</li>
	<li><code>&#39;-&#39;</code> could be used as a unary operation (i.e., <code>&quot;-1&quot;</code> and <code>&quot;-(2 + 3)&quot;</code> is valid).</li>
	<li>There will be no two consecutive operators in the input.</li>
	<li>Every number and running calculation will fit in a signed 32-bit integer.</li>
</ul>

class Solution {
public:
    int f(string s){
        // cout<<s<<" ";
        string res="";
        int n=s.size();
        int ans=0,j=0;
        while(j<n){
            
            string res="";
            if(j<=n-2){
                if(isdigit(s[j])==false && isdigit(s[j+1])==false){
                    if((s[j]=='+' && s[j+1]=='+') || (s[j]=='-' && s[j+1]=='-') ){
                        res+='+';
                    }else{
                        res+='-';
                    }
                    j+=2;
                }else{
                    res+=s[j];
                    j++;
                }
            }else{
                res+=s[j];
                j++;
            }
              
              
              while(j<n && (s[j]!='+' && s[j]!='-')){
                
                   res+=s[j];
                   j++;
              }
              cout<<res<<" ";
           int num=stoi(res);
        //    cout<<res<<" ";
           ans+=num;
              
        }
        return ans;
        
    }






    int calculate(string s1) {
        string s="";
        for(auto it:s1){
            if(it==' ')continue;
            s+=it;
        }
        // cout<<s;
          stack<string>st;
          int n=s.size();
          int j=n-1;

          while(j>=0){
               if(s[j]==')'){
                
                st.push(")");
                j--;
               }else if(s[j]=='('){
                string res="";
                 while(!st.empty() && st.top()!=")"){
                      res+=st.top();
                      st.pop();
                 }
                 st.pop();
                 int x=f(res);
                //  cout<<res<<" ";
                //  cout<<res<<" ";
                //  cout<<x<<" ";
                 st.push(to_string(x));
                //  cout<<st.top();
                j--;
               }else{
                string ac="";
                ac+=s[j];
                // cout<<ac<<" ";
                st.push(ac);
                j--;
               }
          }
        
          string res2="";
          while(!st.empty()){
            res2+=st.top();
            st.pop();
          }
          return f(res2);
    }
};
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