1.07s，tle，BFS算法，不确定原因，根据讨论版已经去掉memset，但是还是不行； 代码在下面：

#include <iostream>
#include <queue>
using namespace std;

const int N = 20;

struct node
{
	int x, y, t;
	string s;
};

bool vis[N][N]{}, p[N][N]{};

static void bfs(int n, int m)
{
	queue <node> q;
	q.push({ 1,1,0,"" });
	p[1][1] = 1;
	int dx[] = { 1,0,-1,0 }, dy[] = { 0,1,0,-1 };
	string ds = "DRUL";
	while (!q.empty())
	{
		int x = q.front().x, y = q.front().y, t = q.front().t;
		string s = q.front().s;
		q.pop();
		if (x == n && y == m)
		{
			cout << t << endl << s << endl;
			return;
		}
		for (int i = 0; i < 4; i++)
		{
			int _x = x + dx[i], _y = y + dy[i];
			if (_x >= 1 && _y >= 1 && _x <= n && _y <= m && (vis[_x][_y] ^ vis[x][y]) && !p[_x][_y])
			{
				p[_x][_y] = 1;
				q.push({ _x,_y,t + 1,s + ds[i] });
			}
		}
	}
	cout << -1 << endl;
}

int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	int T;
	cin >> T;
	while (T--)
	{
		int n, m;
		cin >> n >> m;
		char c;
		for (int i = 1; i <= n; i++) for (int j = 1; j <= m; j++)
		{
			vis[i][j] = 0;
			p[i][j] = 0;
			cin >> c;
			if (c == '1') vis[i][j] = 1;
		}
		bfs(n, m);
	}

	//system("pause");

	return 0;
}