BFS模板

输入一个m×n的地图（含有0和1两种状态，1不能走），起始点和目标点的坐标，找到最短路。

#include <iostream>
#include <queue>
#define SIZE 1000
using namespace std;
queue<int> q_x, q_y, q_pos;
int step[4][2] = {
    {1,0},{0,1},{-1,0},{0,-1}
};
int m, n, board[SIZE][SIZE], start_x, start_y, target_x, target_y;
bool vis[SIZE][SIZE];
void bfs() {
    bool flag = false;
    while (!q_x.empty() && !q_y.empty()) {
        for (int k = 0; k < 4; ++k) {
            int tx = q_x.front() + step[k][0];
            int ty = q_y.front() + step[k][1];
            if (tx < 1 || ty < 1 || tx > n || ty > m)
                continue;
            if (!board[tx][ty] && !vis[tx][ty]) {
                vis[tx][ty] = true;
                q_x.push(tx);
                q_y.push(ty);
                q_pos.push(q_pos.front() + 1);
            }
            if (tx == target_x&&ty == target_y) {
                flag = true;
                break;
            }
        }
        if (flag)
            break;
        q_x.pop();
        q_y.pop();
        q_pos.pop();
    }
    return;
}
int main()
{
    while (cin >> m >> n) {
        for (int i = 1; i <= m; ++i) {
            for (int j = 1; j <= n; ++j) {
                cin >> board[i][j];
            }
        }
        cin >> start_x >> start_y >> target_x >> target_y;
        q_x.push(start_x);
        q_y.push(start_y);
        q_pos.push(0);
        vis[start_x][start_y] = true;
        bfs();
        cout << q_pos.back() << endl;
    }
    return 0;
}