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RobotBoundedInCircle.java
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RobotBoundedInCircle.java
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package Leetcode;
/**
* @author kalpak
*
* 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'.
*
*/
public class RobotBoundedInCircle {
public static boolean isRobotBounded(String instructions) {
int[][] directions = new int[][]{{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
// Initial position
int x = 0;
int y = 0;
int currentIdx = 0;
for (int i = 0; i < 4; i++) {
for(char c : instructions.toCharArray()) {
if(c == 'L')
currentIdx = (currentIdx + 3) % 4;
else if (c == 'R')
currentIdx = (currentIdx + 1) % 4;
else {
x += directions[currentIdx][0];
y += directions[currentIdx][1];
}
}
}
// True if the robot is back to the centre or currentIdx does not face north so we wont have a cycle
return (x == 0 && y == 0) || (currentIdx != 0);
}
public static void main(String[] args) {
String instuctions = "GL";
System.out.println(isRobotBounded(instuctions));
}
}