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1041. Robot Bounded In Circle

Description

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

Solutions

• Java
• C++
• Python
• Go
• TypeScript

• class Solution {
      public boolean isRobotBounded(String instructions) {
          int k = 0;
          int[] dist = new int[4];
          for (int i = 0; i < instructions.length(); ++i) {
              char c = instructions.charAt(i);
              if (c == 'L') {
                  k = (k + 1) % 4;
              } else if (c == 'R') {
                  k = (k + 3) % 4;
              } else {
                  ++dist[k];
              }
          }
          return (dist[0] == dist[2] && dist[1] == dist[3]) || (k != 0);
      }
  }
  

• class Solution {
  public:
      bool isRobotBounded(string instructions) {
          int dist[4]{};
          int k = 0;
          for (char& c : instructions) {
              if (c == 'L') {
                  k = (k + 1) % 4;
              } else if (c == 'R') {
                  k = (k + 3) % 4;
              } else {
                  ++dist[k];
              }
          }
          return (dist[0] == dist[2] && dist[1] == dist[3]) || k;
      }
  };
  

• class Solution:
      def isRobotBounded(self, instructions: str) -> bool:
          k = 0
          dist = [0] * 4
          for c in instructions:
              if c == 'L':
                  k = (k + 1) % 4
              elif c == 'R':
                  k = (k + 3) % 4
              else:
                  dist[k] += 1
          return (dist[0] == dist[2] and dist[1] == dist[3]) or k != 0
  
  

• func isRobotBounded(instructions string) bool {
  	dist := [4]int{}
  	k := 0
  	for _, c := range instructions {
  		if c == 'L' {
  			k = (k + 1) % 4
  		} else if c == 'R' {
  			k = (k + 3) % 4
  		} else {
  			dist[k]++
  		}
  	}
  	return (dist[0] == dist[2] && dist[1] == dist[3]) || k != 0
  }
  

• function isRobotBounded(instructions: string): boolean {
      const dist: number[] = new Array(4).fill(0);
      let k = 0;
      for (const c of instructions) {
          if (c === 'L') {
              k = (k + 1) % 4;
          } else if (c === 'R') {
              k = (k + 3) % 4;
          } else {
              ++dist[k];
          }
      }
      return (dist[0] === dist[2] && dist[1] === dist[3]) || k !== 0;
  }
  
  

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