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 <= 100instructions[i]is'G','L'or,'R'.
class Solution:
def isRobotBounded(self, instructions: str) -> bool:
cur, direction = 0, [0] * 4
for ins in instructions:
if ins == 'L':
cur = (cur + 1) % 4
elif ins == 'R':
cur = (cur + 3) % 4
else:
direction[cur] += 1
return cur != 0 or (
direction[0] == direction[2] and direction[1] == direction[3]
)class Solution {
public boolean isRobotBounded(String instructions) {
int[] direction = new int[4];
int cur = 0;
for (char c : instructions.toCharArray()) {
if (c == 'L') {
cur = (cur + 1) % 4;
} else if (c == 'R') {
cur = (cur + 3) % 4;
} else {
++direction[cur];
}
}
return cur != 0 || (direction[0] == direction[2] && direction[1] == direction[3]);
}
}class Solution {
public:
bool isRobotBounded(string instructions) {
vector<int> direction(4);
int cur = 0;
for (char c : instructions) {
if (c == 'L')
cur = (cur + 1) % 4;
else if (c == 'R')
cur = (cur + 3) % 4;
else
++direction[cur];
}
return cur != 0 || (direction[0] == direction[2] && direction[1] == direction[3]);
}
};func isRobotBounded(instructions string) bool {
direction := make([]int, 4)
cur := 0
for _, ins := range instructions {
if ins == 'L' {
cur = (cur + 1) % 4
} else if ins == 'R' {
cur = (cur + 3) % 4
} else {
direction[cur]++
}
}
return cur != 0 || (direction[0] == direction[2] && direction[1] == direction[3])
}