Solution to "I Failed a Twitter Interview"

import java.util.ArrayList;
import java.util.LinkedList;

public class rainQ{
    public static void main(String [] args){
        int[][] heights = {
                {2,5,1,2,3,4,7,7,6},
                {3,2,1},
                {2,2,1,1,2},
                {5,3,2,1,2,3,4,5,4,3,0,5},
                {2,1,2,1,2},
                {3,2,1,2,1,2,0,2,3},
                {3,1,0,2},
                {},
                {0},
                {1,1},
                {0,0,0},
                {2,5,1,3,1,2,1,7,7,6},
                {5,3,2,1,2,3,4,5,4,3,0,4}
                };


        int[] answers = {10,
                0,
                2,
                23,
                2,
                11,
                3,
                0,
                0,
                0,
                0,
                17};

        rainQ rQ = new rainQ();

        for(int i = 0; i < heights.length; i++){
            boolean correct = (answers[i] == rQ.rainArea(heights[i]));
            if(correct){
                System.out.println("Result " + i + " is " + correct);
            } else {
                System.out.println("Result " + i + " is false.");
            }
            System.out.println();
        }

    }

    public int rainArea(int[] heights){
        // There can't be a wall if there's only 2 elements
        if(heights.length < 3){
            return 0;
        }

        // The derivative of the differences
        int[] changeMatrix = new int[heights.length];

        // Set the first height as the first derivative
        changeMatrix[0] = heights[0];

        boolean trap = false;

        int totalArea = 0, tempArea = 0;
        int maxHeight = 0;
        int length = 0;
        boolean valid = false;

        // Calculate the rest of the heights
        for(int i = 1; i < heights.length; i++){

            changeMatrix[i] = heights[i] - heights[i-1];

            if(trap == true) length++;

            if(trap==false && changeMatrix[i] < 0){
                maxHeight = heights[i-1];
                tempArea += (maxHeight - heights[i]);
                trap = true;
                //System.out.println(tempArea);
            } else if(trap == true && maxHeight-heights[i] > 0 && !(i == heights.length-1)) {
                tempArea += (maxHeight - heights[i]);
                //System.out.println(tempArea);
                if(changeMatrix[i] > 0){
                    valid = true;
                }
            } else if(trap == true && maxHeight-heights[i] <= 0 || i == heights.length-1){
                if(changeMatrix[i]>0){
                    valid = true;
                }

                if(heights[i] < maxHeight){
                    tempArea += length * (heights[i] - maxHeight);
                    //System.out.println(tempArea);
                }

                if(valid) totalArea+=tempArea;
                tempArea = 0;
                trap = false;
                maxHeight = heights[i];
                length = 1;
                valid = false;
            }
        }

        return totalArea;
    }
}