1130 Infix Expression

#include<iostream>
#include<vector>
using namespace std;
struct Node{
	int address;
	string data;
	int left;
	int right;
}node[21];
int Root;
void infix(int root){
	if(root==-1) return;
	if(root!=Root&&(node[root].left!=-1||node[root].right!=-1)) cout<<"(";
	infix(node[root].left);
	cout<<node[root].data;
	infix(node[root].right);
	if(root!=Root&&(node[root].left!=-1||node[root].right!=-1)) cout<<")";
}
int main()
{
	#ifdef ONLINE_JUDGE
	#else
	freopen("in.txt","r",stdin);
	#endif
	int n;
	cin>>n;
	int hash[21]={};
	for(int i=0;i<n;i++){
		int l,r;
		string d;
		cin>>d>>l>>r;
		node[i+1].address=i+1;
		node[i+1].data=d;
		node[i+1].left=l;
		node[i+1].right=r;
	}
	for(int i=1;i<=n;i++){
		if(node[i].left!=-1)
		hash[node[i].left]=1;
		if(node[i].right!=-1)
		hash[node[i].right]=1;
	}
	int root;
	for(int i=1;i<=n;i++){
		if(hash[i]==0){
			root=i;
			break;
		}
	}
	Root=root;
	infix(root);
	return 0;
}