//At each point the water filled will be min(lmax,rmax) - height of that point 
class Solution {
    public int trap(int[] height) {
        if(height.length <= 2)
            return 0;
      int lMax[] = new int[height.length];
      int rMax[] = new int[height.length];
      int result = 0;
        
        lMax[0] = 0;
        int leftMax=height[0];
        
        for(int i=1; i<height.length; i++){
            leftMax = Math.max(leftMax, height[i-1]);
            lMax[i] = leftMax;
        }
        lMax[height.length-1] = leftMax;
        
        rMax[height.length-1] = 0;
        int rightMax = height[height.length-1];
        for(int j=height.length-2; j>=0; j--){
            rightMax = Math.max(rightMax, height[j+1]);
            rMax[j] = rightMax;
        }
        rMax[0] = rightMax;
        
        for(int i=0; i<height.length-1; i++){
            int water = Math.min(lMax[i], rMax[i]) - height[i];
            water = Math.max(water,0);
            result += water ;
        }
        
        return result;
    }
}