Robot Bounded In Circle
Problem Statement - link #
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.
Examples #
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 <= 100instructions[i]is'G','L'or,'R'.
Solutions #
class Solution {
public:
bool isRobotBounded(string instructions) {
int x=0, y=0, i=0;
for(auto ins : instructions){
if(ins == 'G'){
switch(i){
case 0 : //N
y++;
break;
case 1 : //W
x--;
break;
case 2 : //S
y--;
break;
case 3 : //E
x++;
break;
}
}else if(ins == 'L') i = (i+1)%4;
else i = (i+3)%4;
}
return x==0 && y==0 || i != 0;
}
};