可能是 `q.push` 那里的临时变量太多了，改成下面就是 WA#1
```cpp
#include <bits/stdc++.h>
struct node{
int x,y,d;
node()=default;
node(int x,int y,int d) : x(x),y(y),d(d) {}
};
const int MAX = 2005;
int t;
int n,m;
bool vis[MAX][MAX];
char path[MAX][MAX];
std::string a[MAX];
std::array<int,4> dx{-1,1,0,0},dy{0,0,-1,1};
std::array<char,4> dir{'U','D','L','R'};
std::queue<node> q;
bool in(int x,int y){return x >= 1 && x <= n && y >= 1 && y <= m;}
void bfs(){
q.push({1,1,0});
node qwq;
vis[1][1] = true;
path[1][1] = 'S';
int x,y,d;
int i,tx,ty;
while(!q.empty()){
x=q.front().x,y=q.front().y,d=q.front().d;
q.pop();
if(x == n && y == m){
std::cout << d << '\n';
std::vector<int> pathque;
while(path[x][y] != 'S'){
pathque.push_back(path[x][y]);
if(path[x][y] == 'U') x += dx[1],y += dy[1];
if(path[x][y] == 'D') x += dx[0],y += dy[0];
if(path[x][y] == 'L') x += dx[3],y += dy[3];
if(path[x][y] == 'R') x += dx[2],y += dy[2];
}
std::reverse(pathque.begin(),pathque.end());
for(int i:pathque) std::cout << (char)i;
std::cout << '\n';
return;
}
for(i = 0;i < 4;i++){
tx = x + dx[i],ty = y + dy[i];
if(in(tx,ty) && !vis[tx][ty] && a[x][y] != a[tx][ty]){
qwq.x=tx,qwq,y=ty,qwq.d=d+1;
q.push(qwq);
vis[tx][ty] = true;
path[tx][ty] = dir[i];
std::cout << path[tx][ty];
}
}
}
std::cout << -1 << '\n';
}
int main(){
std::ios::sync_with_stdio(false);
std::cin.tie(nullptr);
std::cin >> t;
while(t--){
std::cin >> n >> m;
for(int i = 1;i <= n;i++){
memset(vis[i],0,sizeof(vis[i]));
memset(path[i],0,sizeof(path[i]));
std::cin >> a[i];
a[i] = '.' + a[i];
}
bfs();
}
return 0;
}
```
by xiaoyang111 @ 2024-03-10 08:46:08