Competitive Programming

/**
 * Author: Isaac
 * License:
 * Description: Data structure used for storing information about intervals, or segments.
 * Time: buildTree O(N) - query and updated O(log(n))
 * Status: ???
 * Usage: 
 */
struct node {
   long long int pa;
   long long int pc;
};
node join(node left,node right)
{
    node res;
    int n = min(left.pa, right.pc);
    res.pa = right.pa + left.pa - n;
    res.pc = left.pc + right.pc - n;
    return res;
}
void buildTree(node *tree,string a,int index,int s,int e)
{
    //base case
    if(s>e) return;
    //reached leaf node
    if(s==e)
    {
        if(a[s]==')') { tree[index].pc=1; tree[index].pa=0;} //Base value
        else { tree[index].pa=1;tree[index].pc=0; }
        return ;
    }
    int m = (s+e)/2;
    buildTree(tree,a,2*index,s,m);
    buildTree(tree,a,2*index+1,m+1,e);
    node left = tree[2*index]; node right = tree[2*index+1];
    tree[index]=join(left,right);
	// return left*right;
    return;
}
node query(node *tree,int index,int s,int e,int qs,int qe)
{
    //base case: if query range is outside the node range
    if(qs>e || s>qe) return node{INF,INF}; //Base value
    //complete overlap
    if(s>=qs && e<=qe) return tree[index];
    //now partial overlap case is executed
    int m = (s+e)/2;
    node left = query(tree,2*index,s,m,qs,qe);
    node right = query(tree,2*index+1,m+1,e,qs,qe);
	// return left*right;
    return join(left,right);
}

void updateNode(node *tree,int index,int s,int e,int pos)
{
    if(pos<s || pos>e) return ;
    if(s==e)
    {
        if(tree[index].pc==1) { tree[index].pc=0; tree[index].pa=1; }
        else { tree[index].pc=1; tree[index].pa=0; }
        return;
    }
    int m = (s+e)/2;
    updateNode(tree,2*index,s,m,pos);
    updateNode(tree,2*index+1,m+1,e,pos);
    tree[index] = join(tree[2*index],tree[2*index+1]);
    return;
}
int main()
{
    int n; scanf("%d",&n);
	string a;
	node*tree = new node[4*n+1]; //array to store the segment tree
	int index = 1; //index of 1st node
	int s =0,e=n-1;
	buildTree(tree,a,index,s,e);//now tree has been built
	scanf("%d",&c);
	for(int i=0; i<c;i++){
		int f; scanf("%d",&f);
		if(f==0)
		{
			node aux = query(tree,index,s,e,0,n);
			if(aux.pa==0 && aux.pc==0) printf("YES\n");
			else printf("NO\n");
		}
		else updateNode(tree,index,s,e,f-1);}
    return 0;
}