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/**
 * // 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 Solution {
    public void cleanRoom(Robot robot) {
        DFS(robot, new HashSet<>(), 0, 0, 0);
    }
        
    private void DFS(Robot robot, Set<String> visited, int i, int j, int degrees) {
        String path = i + "->" + j;
        if(!visited.add(path)) return;
        robot.clean();
    
        for(int k = 0; k < 4; k++) {
            if(robot.move()) {
                int x = i, y = j;
                switch(degrees) {
                    case 0:
                        x = i - 1;
                        break;
                    case 90:
                        y = j + 1;
                        break;
                    case 180:
                        x = i + 1;
                        break;
                    case 270:
                        y = j - 1;
                        break;
                    default:
                        break;
                }
                
                DFS(robot, visited, x, y, degrees);
                goBack(robot);
            }
            
            robot.turnRight();
            degrees = (degrees + 90) % 360;    
        }
    }
    
    private void goBack(Robot robot) {
        robot.turnLeft();
        robot.turnLeft();
        robot.move();
        robot.turnLeft();
        robot.turnLeft();
    }    
    
}

/*
int[][] dirs = {{-1,0},{0,-1},{1,0},{0,1}};
more simple
*/

class Solution {
    int[][] dirs = {{-1,0},{0,-1},{1,0},{0,1}};
    
    public void cleanRoom(Robot robot) {
        DFS(robot, new HashSet<>(), 0, 0, 0);
    }
        
    private void DFS(Robot robot, Set<String> visited, int i, int j, int curDir) {
        String path = i + "->" + j;
        if(!visited.add(path)) return;
        robot.clean();

        // curDir => 0: up, 1: left, 2: down, 3: right
        for(int k = 0; k < 4; k++) {
            if(robot.move()) {
                int x = i + dirs[curDir][0]; 
                int y = i + dirs[curDir][1];
                DFS(robot, visited, x, y, curDir);
                goBack(robot);
            }
        
            robot.turnRight();
            //turn 90 degrees
            curDir = (curDir + 1) % 4;    
        } 
    }
    
    private void goBack(Robot robot) {
        robot.turnLeft();
        robot.turnLeft();
        robot.move();
        robot.turnLeft();
        robot.turnLeft();
    }   
}