洛谷P1041 传染病控制

解：搜索......

我们可以每次选择分支少的搜索，或者说，贪心的搜索当前更优的决策。

每一层把能剪的点搞出来，按照度数/SIZ排序，然后依次搜索。加个最优化剪枝就完事了。

 #include <bits/stdc++.h>
 
 const int N = , INF = 0x3f3f3f3f;
 
 struct Edge {
     int nex, v;
 }edge[N << ]; int tp;
 
 int e[N], siz[N], in[N], n, ans = INF;
 int v[N][N];
 bool del[N], vis[N];
 
 inline bool cmp(const int &a, const int &b) {
     //return in[a] > in[b];
     return siz[a] > siz[b];
 }
 
 inline void add(int x, int y) {
     tp++;
     edge[tp].v = y;
     edge[tp].nex = e[x];
     e[x] = tp;
     return;
 }
 
 void DFS_1(int x, int f) {
     siz[x] = ;
     for(int i = e[x]; i; i = edge[i].nex) {
         int y = edge[i].v;
         if(y == f) continue;
         DFS_1(y, x);
         siz[x] += siz[y];
     }
     return;
 }
 
 void DFS(int k, int d) {
     if(k >= ans) return;
     v[d][] = ;
     for(int x = ; x <= n; x++) {
         if(del[x] || !vis[x]) continue;
         /// vis[x]
         for(int i = e[x]; i; i = edge[i].nex) {
             int y = edge[i].v;
             if(vis[y] || del[y]) continue;
             v[d][++v[d][]] = y;
         }
     }
 
     if(!v[d][]) {
         ans = std::min(ans, k);
         return;
     }
 
     std::sort(v[d] + , v[d] + v[d][] + , cmp);
     for(int i = ; i <= v[d][]; i++) {
         vis[v[d][i]] = ;
     }
     k += v[d][] - ;
     for(int i = ; i <= v[d][]; i++) {
         int x = v[d][i];
         del[x] = ;
         vis[x] = ;
         DFS(k, d + );
         vis[x] = ;
         del[x] = ;
     }
     for(int i = ; i <= v[d][]; i++) {
         vis[v[d][i]] = ;
     }
     return;
 }
 
 int main() {
 
 //    freopen("disease.in", "r", stdin);
 //    freopen("disease.out", "w", stdout);
 
     int m;
     scanf("%d%d", &n, &m);
     for(int i = , x, y; i <= m; i++) {
         scanf("%d%d", &x, &y);
         add(x, y); add(y, x);
         in[x]++; in[y]++;
     }
     DFS_1(, );
     vis[] = ;
     DFS(, );
 
     printf("%d\n", ans);
     return ;
 }

AC代码