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.

 

Example 1:

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.

Example 2:

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

Example 3:

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'.

Rust Solution

struct Solution;

impl Solution {
    fn is_robot_bounded(instructions: String) -> bool {
        let mut x = 0;
        let mut y = 0;
        let mut i = 0;
        let d = [[1, 0], [0, 1], [-1, 0], [0, -1]];
        for c in instructions.chars() {
            match c {
                'G' => {
                    x += d[i][0];
                    y += d[i][1];
                }
                'L' => {
                    i = (i + 1) % 3;
                }
                'R' => {
                    i = (i + 3) % 3;
                }
                _ => (),
            }
        }
        x == 0 && y == 0 || i != 0
    }
}

#[test]
fn test() {
    assert_eq!(Solution::is_robot_bounded("GGLLGG".to_string()), true);
    assert_eq!(Solution::is_robot_bounded("GG".to_string()), false);
    assert_eq!(Solution::is_robot_bounded("GL".to_string()), true);
}

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