C++ - Binarno stablo - suma u preorder obilasku

/*

TEMA : Binarno stablo i suma svih cvorova u preorder obilasku

Autor zadatka: Kristijan Burnik

Autor rjesenja: Kristijan Burnik

Datum rjesavanja: 2012-10-06

Primjer:
5
10 20 30 40 50
2
1 2 3
2 4 5

*/
#include <iostream>
#include <cstdlib>
#include <vector>

using namespace std;

typedef struct node {
        int val;
        node *left;
        node *right;
} node;

/////////////////////////////////

int suma(node *p) {
    if (p == NULL) return 0;
    return p->val + suma(p->left) + suma(p->right);
}


int main() {

    int n;
    cin >> n;

    vector < node > stablo;
    stablo.resize( n + 1 ) ;
    for (int i = 1;  i <= n; i++) {
        cin >> stablo[i].val;
    }

    int m;
    cin >> m;
    int p,l,r;
    for (int i = 0 ; i < m ; i++) {
        cin >> p >> l >> r;
        stablo[p].left = &stablo[l];
        stablo[p].right  = &stablo[r];
    }

    cout << "suma: " << suma(&stablo[1]);
    cout << endl;

    system("pause");
    return 0;
}