SGU 321 知道了双端队列，

来源：互联网发布：大数据项目架构设计编辑：程序博客网时间：2024/05/17 04:31

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': ' ');    }}

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