Arraysecondpart.java

import java.util.*;
public class Arraysecondpart{

    // trapping rain water
    public static int trappedrainwater(int height[]){
           int n  = height.length;
        //    calculate maximum left boundary
          int leftMax[] = new int[n]; //helper array
          leftMax[0] = height[0];
          for(int i =1;i<n;i++){
            leftMax[i] = Math.max(height[i],leftMax[i-1]);
          }

        //  calculate maximum left boundary
        int rightmax[] = new int[n];
        rightmax[n-1] = height[n-1];
        for(int i = n-2;i>=0;i--){
            rightmax[i]= Math.max(height[i],rightmax[i+1]);
        }
        
        int tp = 0;
        // loop
        for(int i=0;i<n;i++){
            // water level
            int waterlevel = Math.min(leftMax[i],rightmax[i]);
            // trapped water
            tp += waterlevel-height[i];
        } 
        return tp;
    }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        sc.close();
        int height[] = {4,2,0,6,3,2,5};
        System.out.println(trappedrainwater(height));
    } 
}