find height of binary tree given parent array

/*
the parent array is given where index is the node and its value denotes the parent node. the value of parent[0] i.e root is always -1
*/

#include <bits/stdc++.h>

using namespace std;

//find height of binary tree guven parent aarray
void fillDepth(int a[], int i, int depth[]){
    if(depth[i]) //if already filled
      return;
    if(a[i] == -1) 
      {
          depth[i]=1;
          return;
      }
      //if parent is not filled
    if(depth[a[i]] == 0)
      fillDepth(a,a[i],depth);
      //depth of child is depth of parent + 1
    depth[i] = depth[a[i]] + 1;
}


int height(int a[], int n){
    int depth[n]={0};
    for(int i=0; i<n; i++)
      fillDepth(a,i,depth);
return (*max_element(depth,depth+n));
}


int main()
{
   int a[9] = {-1, 0, 1,6,6,0,0,2,7};
   cout<<height(a,9);
    return 0;
}