题解里只有两篇用到了 priority_queue，都是用的优先队列优化的 Dij 算法，都是这道题其实可以不用 Dij，直接用优先队列来解决。

思路类似洪水填充，优先搜索不需要转弯的情况，这样的话最早搜到的就是答案。

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

struct p
{
	int x;
	int y;
	int t;
	int d;
	bool operator < (const p &x) const
	{
		return x.t < t;
	}
};
priority_queue <p> q;

int n;
char c[114][114];
int dis[114][114];

int bx, by;

int dx[5] = {0, 0,  0, 1, -1};
int dy[5] = {0, 1, -1, 0,  0};

void bfs()
{
	while(q.empty() == 0)
	{
		p t = q.top();
		q.pop();
		if(t.t > dis[t.x][t.y])
			continue;
		dis[t.x][t.y] = t.t;
		if(c[t.x + dx[t.d]][t.y + dy[t.d]] == '.')
			q.push(p{t.x + dx[t.d], t.y + dy[t.d], t.t, t.d});
		for(int i = 1; i <= 4; i = i + 1)
		{
			if(i == t.d)
				continue;
			if(c[t.x + dx[i]][t.y + dy[i]] == '.')
				q.push(p{t.x + dx[i], t.y + dy[i], t.t + 1, i});
		}
	}
}

int main()
{
	cin >> n;
	memset(dis, 0x3f3f3f, sizeof(dis));
	for(int i = 1; i <= n; i = i + 1)
		for(int j = 1; j <= n; j = j + 1)
		{
			cin >> c[i][j];
			if(c[i][j] == 'A')
			{
				q.push(p{i, j, 0, 1});
				q.push(p{i, j, 0, 2});
				q.push(p{i, j, 0, 3});
				q.push(p{i, j, 0, 4});
				dis[i][j] = 0;
			}
			if(c[i][j] == 'B')
			{
				bx = i;
				by = j;
				c[i][j] = '.';
			}
		}
	bfs();
	if(dis[bx][by] != 1061109567)
		cout << dis[bx][by];
	else
		cout << -1;
	return 0;
}