思路: 贪心,
每次删除最上面的边。。
#include<utility> #include<iostream> #include<vector> #include<cstring> #include<deque> #include<cstdio> #include<algorithm> using namespace std; const int M = 200008; deque <int > q; vector <int> vi; int first_edge[M],next_edge[M],to[M],ty[M],sum; void dfs(int u){ if(sum < 0){ sum += 2; ty[q.front()] *= -1; vi.push_back(q.front()); q.pop_front(); } for(int i = first_edge[u] ; i!=-1 ; i = next_edge[i]){ sum += ty[i]; if(ty[i] == -1)q.push_back(i); dfs(to[i]); if(ty[i] == -1){ q.pop_back(); } sum -= ty[i]; } } int main(){ freopen("input.txt","r",stdin); int n,m,u,v; sum = 0; char buf[10]; memset(first_edge,-1,sizeof(first_edge)); scanf("%d",&n); for(int i = 0; i < n-1; i++){ scanf("%d%d%s",&u,&v,buf); next_edge[i] = first_edge[v]; first_edge[v] = i; ty[i] = *buf == 'p' ? 1 : -1; // cout <<ty[i] <<endl; to[i] = u; if(*buf == 'a')scanf("%s",buf); } dfs(1); printf("%d\n",(int)vi.size()); for(int i = 0; i < vi.size(); i++){ printf("%d%c",vi[i]+1, i==vi.size() - 1 ? '\n': ' '); } }
时间: 2024-10-13 21:30:04