这题太难了，不配做黄题

RT 40分TLE，```cpp #include<bits/stdc++.h> using namespace std; int ans=0,n,m,a[100001]; struct node { int x,step; node(int xx,int dep) { x=xx; step=dep; } node() {

}

}; queue q; void bfs(int s) { q.push(node(s,0)); while(!q.empty()) { node now=q.front(); q.pop(); if(now.step==m) { if(now.x==1) { ans++; } continue; } if(now.x+1<=n&&now.x-1>=1) { q.push(node(now.x+1,now.step+1)); q.push(node(now.x-1,now.step+1)); } else if(now.x+1<=n&&now.x-1<1) { q.push(node(now.x+1,now.step+1)); q.push(node(n,now.step+1)); } else if(now.x+1>n&&now.x-1>=1) { q.push(node(1,now.step+1)); q.push(node(now.x-1,now.step+1)); } else { q.push(node(1,now.step+1)); q.push(node(n,now.step+1)); } } } int main() { scanf("%d %d",&n,&m); bfs(1); printf("%d\n",ans); }