Robot Bounded In Circle

On an infinite plane, a robot initially stands at (0, 0) and faces north.  The robot can receive one of three instructions:

The robot performs the instructions given in order, and repeats them forever.

Return true if and only if there exists a circle in the plane such that the robot never leaves the circle.

 

Example 1:

Input: "GGLLGG"
Output: true
Explanation: 
The robot moves from (0,0) to (0,2), turns 180 degrees, and then returns to (0,0).
When repeating these instructions, the robot remains in the circle of radius 2 centered at the origin.
Example 2:

Input: "GG"
Output: false
Explanation: 
The robot moves north indefinitely.
Example 3:

Input: "GL"
Output: true
Explanation: 
The robot moves from (0, 0) -> (0, 1) -> (-1, 1) -> (-1, 0) -> (0, 0) -> ...
 

Note:

  1. 1 <= instructions.length <= 100
  2. instructions[i] is in {'G', 'L', 'R'}

Solution:

class Solution {
    public boolean isRobotBounded(String instructions) {
        Set<List<Integer>> set = new HashSet();
        set.add(Arrays.asList(0, 0, 0));
        int[] curr = new int[]{0, 0, 0};
        int[] dx = new int[]{-1, 0, 1, 0};
        int[] dy = new int[]{0, -1, 0, 1};
        int dir = -1;
        while (dir != curr[2]) {
            dir = curr[2];
            for (char c : instructions.toCharArray()) {
                if (c == 'G') {
                    curr[0] += dx[curr[2]];
                    curr[1] += dy[curr[2]];
                } else if (c == 'L') {
                    curr[2] = (curr[2] + 1) % 4;
                } else {
                    curr[2] = (curr[2] + 3) % 4;
                }
            }
            // return to previous start, means there is cycle
            if (!set.add(Arrays.asList(curr[0], curr[1], curr[2]))) {
                return true;
            }
        }
        return false;
    }
}