LeetCode Q 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 <= instructions.length <= 100
instructions[i]
is in {'G'
,'L'
,'R'
}
Solution
Code:
public boolean isRobotBounded(String instructions) {
int x = 0, y = 0, i = 0;
int[][] dirs = { {0, 1}, {-1, 0}, {0, -1}, {1, 0} };
for (char ch: instructions.toCharArray()) {
if (ch == 'L')
i = (i + 1) % 4;
else if (ch == 'R')
i = (i + 3) % 4;
else {
x += dirs[i][0]; y += dirs[i][1];
}
}
return x == 0 && y == 0 || i != 0;
}