Today I have done leetcode's January LeetCoding Challenge with cpp.

January LeetCoding Challenge 9

Description

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 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'.

Solution

class Solution {
public:
  bool isRobotBounded(string instructions) {
    const int moves[4][2] = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
    int x = 0;
    int y = 0;
    int direction = 0;
    for(int _ = 0; _ < 4; ++_) {
      for(auto instruction : instructions) {
        switch(instruction) {
          case 'G':
            x += moves[direction][1];
            y += moves[direction][0];
            break;
          case 'R':
            direction = (direction + 1) % 4;
            break;
          case 'L':
            direction = (direction + 3) % 4;
            break;
        }
      }
    } 
    return !x && !y;
  }
};

// Accepted
// 116/116 cases passed (5 ms)
// Your runtime beats 7.9 % of cpp submissions
// Your memory usage beats 48.4 % of cpp submissions (6.1 MB)