Leetcode 1041. 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:

• "G": go straight 1 unit;
• "L": turn 90 degrees to the left;
• "R": turn 90 degress to the right.

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'}

Code (Java):

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class Solution {     int[][] dirs = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};     int curX = 0;     int curY = 0;     int curDir = 0;        public boolean isRobotBounded(String instructions) {         if (instructions == null || instructions.length() == 0) {             return true;         }                     for (int count = 0; count < 4; count++) {             for (int i = 0; i < instructions.length(); i++) {                 char c = instructions.charAt(i);                 if (c == 'G') {                     move();                    } else {                     turn(c);                 }             }         }                   return curX == 0 && curY == 0;     }           private void move() {         curX += dirs[curDir][0];         curY += dirs[curDir][1];     }           private void turn(char dir) {         int dirVal = (dir == 'L' ? -1 : 1);         curDir = (curDir + 4 + dirVal) % 4;     } }