Rainwater harvesting problem for a series of walls and facing an issue on some large test cases of wrong answer 130/150 passed

Question

I'm getting a wrong answer on finding the output for a huge input test case. I have thought the logic I have used to be appropriate. Please let me know what is the issue in this code ?

Some input examples to understand the logic are

• Input

N = 4
arr[] = {7,4,0,9}

• Output

10

• Explanation:
  Water trapped by above block of height 4 is 3 units and above block of height 0 is 7 units. So, the total unit of water trapped is 10 units.

• Input

N = 3
arr[] = {6,9,9}

• Output

0

• Explanation:
  No water will be trapped.

long long trappingWater(int arr[], int n) {
  // code here
  vector<pair<int, int>> v;
  long long count = 0;
  for (int i = 0; i < n; i++) {
    if (arr[i] != 0)
      v.push_back({arr[i], i});
  }
  int z = v.size();
  for (int i = z - 1; i >= 1; i--) {
    int end_index = v[i].second;
    int end_wall = v[i].first;

    int maxer = 0;
    for (int j = i - 1; j >= 0; j--) {
      int start_index = v[j].second;
      int start_wall = v[j].first;
      long long temp = 0;
      if (end_index - start_index >= 2)
        temp =
            (end_index - start_index - 1) * (min(end_wall, start_wall) - maxer);

      if (temp > 0)
        count += temp;

      maxer = max(start_wall, maxer);

      if (start_wall >= end_wall)
        break;
    }
    // cout<<count<<endl;
  }
  return count;
}

this is the question link run/submit with this one https://practice.geeksforgeeks.org/problems/trapping-rain-water-1587115621/1#

Answer 1

found the solution it was basically a integer overflow but instead of crashing or giving an error it gave a garbage value , so it ran now

the solution is to change the value of temp to temp=1LL*(end_index - start_index -1 )1LL( min(end_wall,start_wall)-maxer );