Arrays leetcode trappedrainwater.java

/*
 *    Trapping Rainwater
 * 
 *  [Problem] -> Given n non-negative integers representing an elevation map where 
 *               the width of each bar is 1, compute how much water it can trap after raining.
 *               height=[4,2,0,6,3,2,5]
 * 
 */


public class TrappingRainwaterVVI {
    
    public static int trappedRainwater(int height[]) {
        
        int n=height.length;
        // calculate left max boundary - array
        int leftMax[]=new int[n];
        leftMax[0]=height[0];
        for(int i=1; i<n; i++){
            leftMax[i] = Math.max(height[i], leftMax[i-1]);
        }
        
        // calculate right max boundary - array
        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]);
        }

        // loop
        int trappedWater=0;
        for(int i=0; i<n; i++){
            // waterLavel = min(leftmax bar , rightmax bar)
            int waterLevel= Math.min(leftMax[i], rightMax[i]);

            // trapped water = waterLevel - height[i]
            trappedWater  = trappedWater + ( waterLevel-height[i]);
        }
       return trappedWater;
    }

    public static void main(String[] args) {
        int height[]={4,2,0,6,3,2,5};
        int trappedWater=trappedRainwater(height);
        System.out.println("After raining water trap : " + trappedWater);
    }
}

/*
 *    Output:
 *    After raining water trap : 11
 */