489. Robot Room Cleaner

/**
 * // This is the robot's control interface.
 * // You should not implement it, or speculate about its implementation
 * interface Robot {
 *     // Returns true if the cell in front is open and robot moves into the cell.
 *     // Returns false if the cell in front is blocked and robot stays in the current cell.
 *     public boolean move();
 *
 *     // Robot will stay in the same cell after calling turnLeft/turnRight.
 *     // Each turn will be 90 degrees.
 *     public void turnLeft();
 *     public void turnRight();
 *
 *     // Clean the current cell.
 *     public void clean();
 * }
 */
 class Coord {
    int r, c;

    Coord (int r, int c) {
        this.r = r;
        this.c = c;
    }

    @Override
    public int hashCode() {
        return r * 1000 + c;
    }

    @Override
    public boolean equals(Object other) {
        Coord coord = (Coord) other;
        return coord.r == r && coord.c == c;
    }

     @Override
     public String toString() {
         return "<" + r + ", " + c + ">";
     }
}

class Solution {

    int[] rows = {-1, 0, 1, 0};
    int[] columns = {0, 1, 0, -1};
    // Direction-> 0: Up, 1: Right, 2: Down, 3: Left

    public void cleanRoom(Robot robot) {
        dfs(new HashSet<Coord>(), robot, 0, new Coord(0, 0));
    }
      private void goBack(Robot robot) {

        robot.turnRight();
        robot.turnRight();
        // turn 180 degree
        robot.move();
        // move forward
        robot.turnRight();
        robot.turnRight();
        // turn 180 degree again
      }

    private void dfs(HashSet<Coord> visited, Robot robot, int direction, Coord currentCoord){

        if(visited.contains(currentCoord)) return;
        visited.add(currentCoord);
        robot.clean();
        // clean the current cell.

        for (int i = 0; i < 4; i++) {
           int newDirection = (direction + i) % 4;
           int newRow = currentCoord.r + rows[newDirection];
           int newCol = currentCoord.c + columns[newDirection];
           if (robot.move()) {
                dfs(visited, robot, newDirection, new Coord(newRow, newCol));
                goBack(robot);
           }
           robot.turnRight();
        }
    }

}