BZOJ2314 士兵的放置

树形DP，恩然后就不会了。。。

先写了个错的离谱程序。。。果然WA了

然后开始乱搞，欸，对了！

令f[i], g[i], h[i]分别表示i号节点自己放士兵，被儿子上的士兵控制，不被儿子上的士兵控制但被父亲上的士兵控制的情况下，以i为子树中最少的士兵数

F[i], G[i], H[i]表示对应的方案数，然后这方程写的沁人心脾。。。看程序吧

 /**************************************************************
     Problem: 2314
     User: rausen
     Language: C++
     Result: Accepted
     Time:3224 ms
     Memory:99512 kb
 ****************************************************************/

 #include <cstdio>
 #include <algorithm>

 using namespace std;
 typedef long long ll;
 const int N = 5e5 + ;
 const int inf = 1e9;
 const int mod = ;
 const int Maxlen = N * ;

 struct edge {
     int next, to;
     edge() {}
     edge(int _n, int _t) : next(_n), to(_t) {}
 } e[N << ];

 int n;
 int first[N], tot;
 ll f[N], g[N], h[N];
 ll F[N], G[N], H[N];
 ll ans;
 bool vis[N];
 char buf[Maxlen], *c = buf;
 int Len;

 inline int read() {
     int x = ;
     while (*c < '' || '' < *c) ++c;
     while ('' <= *c && *c <= '')
         x = x *  + *c - '', ++c;
     return x;
 }

 inline void Add_Edges(int x, int y) {
     e[++tot] = edge(first[x], y), first[x] = tot;
     e[++tot] = edge(first[y], x), first[y] = tot;
 }

 #define y e[x].to
 void dfs(int p) {
     int x, mn;
     ll t;
     vis[p] = ;
     f[p] = , g[p] = inf, h[p] = ;
     F[p] = G[p] = H[p] = ;
     for (x = first[p]; x; x = e[x].next)
         if (!vis[y]) {
             dfs(y);

             mn = min(min(f[y], g[y]), h[y]), t = ;
             if (f[y] == mn) t += F[y];
             if (g[y] == mn) t += G[y];
             if (h[y] == mn) t += H[y];
             f[p] += mn, (F[p] *= t) %= mod;

             mn = min(min(g[p] + f[y], g[p] + g[y]), h[p] + f[y]), t = ;
             if (g[p] + f[y] == mn) t += G[p] * F[y];
             if (g[p] + g[y] == mn) t += G[p] * G[y];
             if (h[p] + f[y] == mn) t += H[p] * F[y];
             g[p] = mn, G[p] = t % mod;

             h[p] += g[y], (H[p] *= G[y]) %= mod;
         }
 }
 #undef y

 int main() {
     Len = fread(c, , Maxlen, stdin);
     buf[Len] = '\0';
     int i, x, y;
     n = read();
     for (i = ; i < n; ++i) {
         x = read(), y = read();
         Add_Edges(x, y);
     }
     dfs();
     printf("%lld\n", min(f[], g[]));
     printf("%lld\n", f[] == g[] ? (F[] + G[]) % mod : f[] < g[] ? F[] : G[]);
     return ;
 }