Leetcode 874: Walking Robot Simulation

https://leetcode.com/problems/walking-robot-simulation/description/

Notes:

This question is pretty straightforward, as labeled as easy.

The first step, we can put all the obstacles into a set. In this way, we can easily to tell whether it is a obstacle or not.

The second, we need a variable to represents the direction. There are four directions: north, east, south, and west, which can be labeled by 0, 1, 2, and 3, respectively.

Then turn left can be updated by (d + 3) % 4, and turn right can be updated as (d + 1)%4.

When d = 0, the x is updated by + 0, and y is updated by + 1;
when d = 1,        x                       + 1,                                 + 0;
when d = 2,        x                       + 0,                                 -  1;
when d = 3,        x                       - 1,                                 + 0;

Thus, we can simply these by using a one-dimensional direction array.

See the code below:

class Solution {
public:
    int robotSim(vector<int>& commands, vector<vector<int>>& obstacles) {
        int res = 0;
        set<vector<int>> ob;
        for(auto &a : obstacles) ob.insert(a);
        int x = 0, y = 0, d = 0;
        vector<int> dirs={0, 1, 0, -1, 0};
        for(auto &a : commands) {
            if(a == -2) d = (d + 3)%4;
            else if(a == -1) d = (d + 1)%4;
            else {
                for(int i=0; i<a; ++i) {
                    if(ob.count({x + dirs[d], y + dirs[d+1]})) break;
                    else {
                        x += dirs[d];
                        y += dirs[d+1];
                    }
                    res = max(res, x*x + y*y);
                }
            }
        }
        return res;
    }
};