C++ Segmentation fault while building a segment tree - c++

Question

I am trying to build a segment tree to get to calculate sub array with max sum in given interval of an array... (for each query)
I am getting segmentation fault in the function "void build()" I have checked with array size....this works fine when size are small...but segmentation fault occurs for larger array size..
thanks in advance:)
success test case:
3
-1 2 3
1
1 2
2
seg fault test case:
90
324 3 23 -234 32 -4 324 435 -5775
324 3 23 -234 32 -4 324 435 -5775
324 3 23 -234 32 -4 324 435 -5775
324 3 23 -234 32 -4 324 435 -5775
324 3 23 -234 32 -4 324 435 -5775
324 3 23 -234 32 -4 324 435 -5775
324 3 23 -234 32 -4 324 435 -5775
324 3 23 -234 32 -4 324 435 -5775
324 3 23 -234 32 -4 324 435 -5775
324 3 23 -234 32 -4 324 435 -5775
9
1 4
3 5
5 9
1 40
2 50
5 90
10 40
50 90
30 50
<pre><code>
#include<iostream>
#include<limits.h>
#include<math.h>
using namespace std;
typedef struct node node;
struct node{
long int sum;
long int lbest;
long int rbest;
long int max;
};
void build(node *tree , long int n , long int start , long int end , long int *ar ){
if(start == end){
tree[n].sum = tree[n].lbest = tree[n].rbest = tree[n].max = ar[start];
return ;
}
else{
long int mid = (start + end)/2;
build(tree , (2*n) +1 , start , mid , ar);
build(tree , (2*n) +2 , mid+1 , end , ar);
tree[n].sum = tree[2*n+1].sum + tree[2*n+2].sum;
tree[n].lbest = max(tree[2*n+1].lbest , tree[2*n+1].sum + tree[2*n+2].lbest);
tree[n].rbest = max(tree[2*n+2].rbest , tree[2*n+2].sum + tree[2*n+1].rbest);
tree[n].max = max(tree[n].sum , max(tree[n].lbest , tree[n].rbest));
// cout<<start<<" "<<end<<" -- "<<n<<" ";
// cout<<" else "<<endl;
}
}
long int query(node *tree , long int n , long int l , long int r , long int start , long int end){
if(l > end || r < start)return INT_MIN;
if(start >= l && end <= r)return tree[n].max;
long int mid = (start + end)/2;
return max(query(tree, (n*2)+1 , l , r , start , mid) , query(tree , 2*n+2 , l , r, mid +1 , end));
}
int main(){
// ios_base::sync_with_stdio(false);
// cin.tie(NULL);
// cout.tie(NULL);
long int n , q;
scanf("%ld" , &n);
long int ar[n];
for(long int i = 0 ;i< n ; i++)cin>>ar[i];
long int nn = n*2;
node tree[nn+1];
build(tree, 0 ,0,n-1 ,ar);
scanf("%ld" , &q);
while(q--){
long a , b ;
scanf("%ld %ld" , &a ,&b);
a-- ;b--;
printf("%ld\n" ,query(tree, 0 , a , b, 0 , n-1));
}
return 0;
}
</code></pre>

Answer 1

The minimum size of segment tree must be 2^(ceil(log(n))+1)-1 where n is number of elements in array .
Just increase the segment tree size to 3*n .
Source : https://www.geeksforgeeks.org/segment-tree-set-1-range-minimum-query/