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1041. Robot Bounded In Circle.md

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1041. Robot Bounded In Circle

leetcode Daily Challenge on September 17th, 2020.

Difficulty : Medium

Related Topics : Math

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

  • mine
    • Java
      • Runtime: 9 ms, faster than 5.22%, Memory Usage: 39.9 MB, less than 5.16% of Java online submissions 
        // O(N)time
// O(N)space
public boolean isRobotBounded(String ins) {
    int[][] dir = new int[4][2];
    dir[0] = new int[]{1,0};
    dir[1] = new int[]{0,-1};
    dir[2] = new int[]{-1,0};
    dir[3] = new int[]{0,1};
    int s = 3;
    int x = 0, y = 0;
    int i = 0;
    char[] arr = ins.toCharArray();
    Set<String> set = new HashSet<>();
    set.add("0-0");
    while(i < 4){
        i++;
        for(char c : arr){
            if(c == 'G'){
                x += dir[s][0];
                y += dir[s][1];
            }else if(c == 'L'){
                s = (s + 3) % 4;
            }else{
                s = (s + 1) % 4;
            }
        }
        String t = x + "-" + y;
        if(set.contains(t)){
            return true;
        }else{
            set.add(t);
        }
    }
    return false;
}
  • the most votes
  • Runtime: 1 ms, faster than 34.44%, Memory Usage: 39.1 MB, less than 13.97% of Java online submissions 
    // O(N)time
// O(1)space
public boolean isRobotBounded(String ins) {
    int x = 0, y = 0, i = 0, d[][] = {{0, 1}, {1, 0}, {0, -1}, { -1, 0}};
    for (int j = 0; j < ins.length(); ++j)
        if (ins.charAt(j) == 'R')
            i = (i + 1) % 4;
        else if (ins.charAt(j) == 'L')
            i = (i + 3) % 4;
        else {
            x += d[i][0]; y += d[i][1];
        }
    return x == 0 && y == 0 || i > 0;
}