class Solution{

    // arr: input array

    // n: size of array

    // Function to find the trapped water between the blocks.

    static long trappingWater(int arr[], int n) { 

        // Your code here

        long cnt = 0;

        long ml = 0, mr = 0;

        int l=0, r=n-1;

        while(l<=r){

            if(arr[l]<arr[r]){

                if(arr[l]<ml){

                    cnt +=ml-arr[l];

                }

                else{

                    ml = arr[l];

                }

                l++;

            }

            else{

                if(arr[r]<mr){

                    cnt += mr-arr[r];

                }

                else{

                    mr = arr[r];

                }

                r--;

            }

        }

        return cnt;

    } 

}