在 Matrix 中查找机器人未针对给定运动访问的单元格

给定一个整数N，它表示矩阵的大小为N*N。有一个机器人放置在矩阵的左上角 (0, 0) 上，机器人的运动方向为 (N, S, W, E, NE, NW, SE, SW 表示北，还给出了南、西、东、东北、西北、东南、西南)和特定方向运动的持续时间。任务是在所有风结束时机器人移动完成后，找到矩阵中未访问的单元格。

注意：机器人只能访问一个单元格一次。如果在任何时候机器人无法移动，则它将停留在当前位置。此外，机器人每秒可以移动一个。

例子：

Input: N = 3, move[] = {(0, SE), (2, N)}
Output: 4
Explanation:
 

Input: 
N = 5,  move[] = 
{(0, SE), 
(1, NE), 
(2, E), 
(6, SW), 
(15, N), 
(20, W)}
Output: 
13
Explanation: 
After the movements of the robot, there are 13 Cells unvisited.

方法：思路是用递归来解决这个问题。最初，将机器人的当前位置设置为 (0, 0)。按照给定的方向开始机器人的运动，并将单元格标记为矩阵的访问过。最后，在机器人标记完成移动后，计算矩阵中未被标记为已访问的单元格

下面的代码实现了上面讨论的方法：

C++

// C++ implementation to find the
// unvisited cells of the matrix
 
#include 
 
using namespace std;
 
// Dimension
// of the board
int n;
 
// Current location
// of the robot
int curr_i = 0, curr_j = 0;
 
// Function to move the robot
void moveRobot(
    int n, int i,
    int j, int dx,
    int dy, int& duration,
    vector >& visited)
{
 
    // if the robot tends to move
    // out of the board
    // or tends to visit an
    // already visited position
    // or the wind direction is changed
    if (i < 0 || i >= n || j < 0 || j >= n
        || visited[i][j] == true
        || duration == 0) {
 
        // the robot can't move further
        // under the influence of
        // current wind direction
        return;
    }
 
    // Change the current location
    // and mark the current
    // position as visited
    curr_i = i;
    curr_j = j;
    visited[i][j] = true;
 
    // One second passed
    // visiting this position
    duration--;
 
    moveRobot(n, i + dx, j + dy, dx,
              dy, duration, visited);
}
 
// Function to find the unvisited
// cells of the matrix after movement
void findUnvisited(
    int p,
    vector > periods)
{
    // nXn matrix to store the
    // visited state of positions
    vector > visited;
 
    // map to store the wind directions
    unordered_map > mp
        = { { "N", { -1, 0 } },
            { "S", { 1, 0 } },
            { "E", { 0, 1 } },
            { "W", { 0, -1 } },
            { "NE", { -1, 1 } },
            { "NW", { -1, -1 } },
            { "SE", { 1, 1 } },
            { "SW", { 1, -1 } } };
 
    // Initially all of the
    // positions are unvisited
    for (int i = 0; i < n; i++) {
        visited.push_back(vector{});
        for (int j = 0; j < n; j++) {
            visited[i].push_back(false);
        }
    }
 
    for (int i = 0; i < p; i++) {
        string dir = periods[i].second;
        int dx = mp[dir][0];
        int dy = mp[dir][1];
 
        // duration for the which the
        // current direction of wind exists
        int duration;
 
        if (i < p - 1) {
            // difference of the start time
            // of current wind direction
            // and start time of the
            // upcoming wind direction
            duration
                = periods[i + 1].first
                  - periods[i].first;
        }
        else {
            // the maximum time for which
            // a robot can move is
            // equal to the diagonal
            // length of the square board
            duration = sqrt(2) * n;
        }
 
        // If its possible to move
        // the robot once in the
        // direction of wind, then
        // move it once and call the
        // recursive function for
        // further movements
        int next_i = curr_i + dx;
        int next_j = curr_j + dy;
 
        if (next_i >= 0
            && next_i < n
            && next_j >= 0
            && next_j < n
            && visited[next_i][next_j] == false
            && duration > 0) {
            moveRobot(n, next_i,
                      next_j, dx, dy,
                      duration, visited);
        }
    }
 
    // Variable to store the
    // number of unvisited positions
    int not_visited = 0;
 
    // traverse over the matrix and
    // keep counting the unvisited positions
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            if (visited[i][j] == false) {
                not_visited++;
            }
        }
    }
 
    cout << not_visited << "\n";
}
 
// Driver Code
int main()
{
 
    // Dimension of the board
    n = 5;
 
    // number of periods
    int p = 6;
 
    // vector of pairs
    vector > periods(p);
    periods[0] = { 0, "SE" };
    periods[1] = { 1, "NE" };
    periods[2] = { 2, "E" };
    periods[3] = { 6, "SW" };
    periods[4] = { 15, "N" };
    periods[5] = { 20, "W" };
 
    // Function Call
    findUnvisited(p, periods);
    return 0;
}

输出：

13

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