<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:
    long long int calc(vector<string> st){
    
        long long int ans=0;
        bool plusCheck=true;

        for(int i=st.size()-1;i>=0;i--){
            string x=st[i];
            if(x=="+"){
                plusCheck=true;
            }
            else if(x=="-"){
                plusCheck=false;

            }
            else{
                if(plusCheck){
                    ans+=(stoll(x));
                }
                else{
                    ans-=(stoll(x));
                }

            }
        }
        return ans;
    }

    int calculate(string s) {
        int n=s.size();
        vector<string> st;
        int i=0;
        while(i<n){
            string tempo="";
            tempo+=s[i];
            if(tempo==" "){
                i++;
                continue;
            }
            if(tempo=="("){
                st.push_back(tempo);
            }
            else if(tempo==")"){
                int temp=0;
                vector<string> s2;
                
                while(st.size() and st.back()!="("){
                    string x=st.back();
                    st.pop_back();
                    s2.push_back(x);
                }
                long long int val=calc(s2);
                st.pop_back();
                string tempo=to_string(val);
                st.push_back(tempo);
            }
            else if(tempo=="+" or tempo=="-"){
                st.push_back(tempo);
            }
            else{
                string valStorer="";
                valStorer+=tempo;
                
                while(i+1<=n-1 ){
                    string tempo="";
                    tempo+=s[i+1];
                    if(tempo==" "){
                        i++;
                        continue;
                    }
                    else if(s[i+1]-'0'<=9 and s[i+1]-'0'>=0){
                        valStorer+=s[i+1];
                        i++;
                    }
                    else{
                        break;

                    }       
                }
                st.push_back(valStorer);

            }

            i++;
        }

        vector<string> s2;
        while(st.size()){
            string temp=st.back();
            st.pop_back();
            s2.push_back(temp);

        }
        int ans=calc(s2);
        return ans;

        return 0;
        
    }
};
52493