TRAPPING WATER

 public class trappingwater {

    public static int trappingwater(int height[]) {

        // LEFT MAX BOUNDARY

        int leftMax[] = new int[height.length];

        leftMax[0] = height[0];

        for (int i = 1; i < height.length; i++) {

            leftMax[i] = Math.max(height[i], leftMax[i - 1]);

        }

        // RIGHT MAX BOUNDARY

        int rightMax[] = new int[height.length];

        rightMax[height.length - 1] = height[height.length - 1];

        for (int i = height.length - 2; i >= 0; i--) {

            rightMax[i] = Math.max(height[i], rightMax[i + 1]);

        }

        // WATER LEVEL

        // waterlevel=min(leftmax-right max)

        int trappedWater = 0;

        for (int i = 0; i < height.length; i++) {

            int waterlevel = Math.min(leftMax[i], rightMax[i]);

            trappedWater += waterlevel - height[i];

        }

        return trappedWater;

    }

    public static void main(String[] args) {

        int height[] = { 4, 2, 0, 6, 3, 2, 5 };

        System.out.println(trappingwater(height));

    }

}