1041 - Robot Bounded in Circle

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 degrees 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

Examples

Input: instructions = "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.

Input: instructions = "GG" Output: false Explanation: The robot moves north indefinitely.

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

Constraints

1 <= instructions.length <= 100 instructions[i] is 'G', 'L' or, 'R'.

Java Solution

class Solution {
    public boolean isRobotBounded(String instructions) {
        int heading = 0; // North = 0, East = 1, South = 2, West = 3
        int x = 0;
        int y = 0;
        
        for(char instruction : instructions.toCharArray()) {
            if(instruction == 'G') {
                if(heading == 0) y++;
                else if(heading == 2) y--;
                else if(heading == 1) x++;
                else if(heading == 3) x--;
            } 
            else if(instruction == 'L'){
                if(heading == 0) heading = 3;
                else heading--;
            } 
            else if(instruction == 'R') {
                if(heading == 3) heading = 0;
                else heading++;
            }
        }
        
        if((x==0 && y==0) || heading != 0) return true;
        
        return false;
    }
}