README.md

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'}

Solutions (Rust)

1. Solution

impl Solution {
    pub fn is_robot_bounded(instructions: String) -> bool {
        let mut position = (0, 0);
        let mut direction = 0;

        for ins in instructions.chars() {
            match (ins, direction % 4) {
                ('G', 0) => position.1 += 1,
                ('G', 1) => position.0 += 1,
                ('G', 2) => position.1 -= 1,
                ('G', 3) => position.0 -= 1,
                ('L', _) => direction += 3,
                _ => direction += 1,
            }
        }

        position == (0, 0) || direction % 4 != 0
    }
}