LeetCode1041. Robot Bounded In Circle

文章目录

• • 一、题目
  • 二、题解

    一、题目

    On an infinite plane, a robot initially stands at (0, 0) and faces north. Note that:

    （）

    The north direction is the positive direction of the y-axis.

    The south direction is the negative direction of the y-axis.

    （）

    The east direction is the positive direction of the x-axis.

    The west direction is the negative direction of the x-axis.

    The robot can receive one of three instructions:

    “G”: go straight 1 unit.

    “L”: turn 90 degrees to the left (i.e., anti-clockwise direction).

    “R”: turn 90 degrees to the right (i.e., clockwise direction).

    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 is initially at (0, 0) facing the north direction.

    “G”: move one step. Position: (0, 1). Direction: North.

    “G”: move one step. Position: (0, 2). Direction: North.

    “L”: turn 90 degrees anti-clockwise. Position: (0, 2). Direction: West.

    “L”: turn 90 degrees anti-clockwise. Position: (0, 2). Direction: South.

    “G”: move one step. Position: (0, 1). Direction: South.

    “G”: move one step. Position: (0, 0). Direction: South.

    Repeating the instructions, the robot goes into the cycle: (0, 0) --> (0, 1) --> (0, 2) --> (0, 1) --> (0, 0).

    Based on that, we return true.

    Example 2:

    Input: instructions = “GG”

    Output: false

    Explanation: The robot is initially at (0, 0) facing the north direction.

    “G”: move one step. Position: (0, 1). Direction: North.

    “G”: move one step. Position: (0, 2). Direction: North.

    Repeating the instructions, keeps advancing in the north direction and does not go into cycles.

    Based on that, we return false.

    Example 3:

    Input: instructions = “GL”

    Output: true

    Explanation: The robot is initially at (0, 0) facing the north direction.

    “G”: move one step. Position: (0, 1). Direction: North.

    “L”: turn 90 degrees anti-clockwise. Position: (0, 1). Direction: West.

    “G”: move one step. Position: (-1, 1). Direction: West.

    “L”: turn 90 degrees anti-clockwise. Position: (-1, 1). Direction: South.

    “G”: move one step. Position: (-1, 0). Direction: South.

    “L”: turn 90 degrees anti-clockwise. Position: (-1, 0). Direction: East.

    “G”: move one step. Position: (0, 0). Direction: East.

    “L”: turn 90 degrees anti-clockwise. Position: (0, 0). Direction: North.

    Repeating the instructions, the robot goes into the cycle: (0, 0) --> (0, 1) --> (-1, 1) --> (-1, 0) --> (0, 0).

    Based on that, we return true.

    Constraints:

    1 public: bool isRobotBounded(string instructions) { int n = instructions.size(); vector{0,1},{1,0},{0,-1},{-1,0}}; int direction = 0; int x = 0,y = 0; for(int i = 0;i