Trapping Rain Water

public class Solution {
    public int trap(int[] A) {
        if(A==null || A.length<3) return 0;
        int res=0, curV = 0, max=A[0];
        int[] mL = new int[A.length];
        int[] mR = new int[A.length];
        
        for(int i=1; i<A.length-1; i++){
            mL[i] = max;
            max = Math.max(A[i],max);
        }
        max = A[A.length-1];
        for(int j=A.length-2; j>=0; j--){
            mR[j] =max;
            max = Math.max(A[j], max);
            curV = Math.min(mL[j], mR[j])-A[j];
            if(curV>0) 
                res += curV;
        }
        
        return res;
    }
}