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  • 死亡的颂唱者 NOIP模拟 贪心 DFS

    把s当作树根,把无根树转化为有根树,然后遍历一个层次图,贪心地取每个叶子结点的第k个父亲节点即可。

     1 #include<cstdio>
     2 #include<cstring>
     3 #include<vector>
     4 using namespace std;
     5 template<class T> inline void read(T &_a){
     6     bool f=0;int _ch=getchar();_a=0;
     7     while(_ch<'0' || _ch>'9'){if(_ch=='-')f=1;_ch=getchar();}
     8     while(_ch>='0' && _ch<='9'){_a=(_a<<1)+(_a<<3)+_ch-'0';_ch=getchar();}
     9     if(f)_a=-_a;
    10 }
    11 
    12 const int maxn=1001;
    13 struct edge{int to,next;}w[maxn<<1];
    14 int T,n,s,k,egcnt,head[maxn],nowu,nowcnt,dep[maxn],fa[maxn],deg[maxn];
    15 bool vis[maxn];
    16 vector<int>node[maxn];
    17 
    18 inline void addedge(int from,int to)
    19 {
    20     w[++egcnt].to=to;
    21     w[egcnt].next=head[from];
    22     head[from]=egcnt;
    23     w[++egcnt].to=from;
    24     w[egcnt].next=head[to];
    25     head[to]=egcnt;
    26     ++deg[from];
    27     ++deg[to];
    28 }
    29 
    30 void dfs_dep(int u,int fr)
    31 {
    32     dep[u]=dep[fr]+1;
    33     fa[u]=fr;
    34     if(deg[u]==1) node[dep[u]].push_back(u);
    35     for (register int i=head[u];i;i=w[i].next)
    36         if(dep[w[i].to]==-1) dfs_dep(w[i].to,u);
    37 }
    38 
    39 void dfs(int u,int fr,int cnt)
    40 {
    41     vis[u]=true;
    42     if(cnt==k) return ;
    43     for (register int i=head[u];i;i=w[i].next)
    44         if(w[i].to!=fr) dfs(w[i].to,u,cnt+1);
    45 }
    46 
    47 inline int rush()
    48 {
    49     int res=0;
    50     for (register int i=n-1;i>k;--i)
    51     {
    52         for (register int v=node[i].size()-1;v>=0;--v)
    53             if(!vis[node[i][v]])
    54             {
    55                 ++res;
    56                 int u=node[i][v];
    57                 for (register int j=1;j<=k;++j) u=fa[u];
    58                 dfs(u,0,0);
    59             }
    60     }
    61     return res;
    62 }
    63 
    64 int main()
    65 {
    66     freopen("singer.in","r",stdin);
    67     freopen("singer.out","w",stdout);
    68     for (read(T);T;--T)
    69     {
    70         memset(head,0,sizeof(head));
    71         memset(vis,0,sizeof(vis));
    72         memset(deg,0,sizeof(deg));
    73         memset(dep,-1,sizeof(dep));
    74         egcnt=0;
    75         read(n); read(s); read(k);
    76         for (register int i=0;i<n;++i) node[i].clear();
    77         for (register int i=1,a,b;i<n;++i) read(a),read(b),addedge(a,b);
    78         dfs_dep(s,0);
    79         printf("%d
    ",rush());
    80     }
    81     fclose(stdin);
    82     fclose(stdout);
    83     return 0;
    84 }
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  • 原文地址:https://www.cnblogs.com/jaywang/p/7745319.html
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