直接搜o(nmk)会超时，需要剪枝

#include <bits/stdc++.h>
using namespace std;

const int N = 1010;

char g[N][N];
int d[N][N];
int dx[] = {1, 0, -1, 0};
int dy[] = {0, 1, 0, -1};
int n, m, k;
int sx, sy, ex, ey;


void bfs(){
    memset(d, -1, sizeof d);
    queue<pair<int, int>> q;
    q.push({sx, sy});
    d[sx][sy] = 0;

    while (q.size()) {
        auto p = q.front();
        q.pop();
        int px = p.first, py = p.second;

        for (int i = 0; i < 4; i++) {
            int x = px, y = py;
            for (int j = 1; j <= k; j++){
                x += dx[i];
                y += dy[i];
                if (x >= 1 && x <= n && y >= 1 && y <= m) {
                    if (d[x][y] != -1 && d[x][y] <= d[px][py]) break;//找到比当前路径更短的路径，直接弹出当前点
                    else if (d[x][y] == -1) {
                        if (g[x][y] == '#') break;
                        d[x][y] = d[px][py] + 1;
                        q.push({x, y});
                    }
                }
            }
        }
    }
}

int main(){
    cin >> n >> m >> k;
    string s;
    for (int i = 1; i <= n; i++) {
        cin >> s;
        for (int j = 1; j <= m; j++) { 
            g[i][j] = s[j-1];
        }
    }

    cin >> sx >> sy >> ex >> ey;
    bfs();
    cout << d[ex][ey];
    return 0;
}