poj3342 Party at Hali-Bula

树形dp题，状态转移方程应该很好推，但一定要细心。

http://poj.org/problem?id=3342

 #include <cstdio>
 #include <cstring>
 #include <algorithm>
 #include <string>
 #include <map>
 using namespace std;
 const int maxn =  + ;
 char buf[maxn];
 struct Edge{
     int to, next;
 }edge[maxn << ];
 int head[maxn], N;
 map<string, int> mapi;
 int n, k;
 int dp[maxn][];
 int o[maxn][];
 int get_str(char *dest){
     int cnt = ;
     char ch;
     do{
         ch = getchar();
     }while(ch != EOF && (ch == ' ' || ch == '\n'));
     if(ch == EOF) return ;
     dest[cnt++] = ch;
     while((ch = getchar()) != ' ' && ch != '\n' && ch != EOF) dest[cnt++] = ch;
     dest[cnt] = '\0';
     return cnt;
 }

 void addEdge(int u, int v){
     edge[N].next = head[u];
     edge[N].to = v;
     head[u] = N++;
 }

 void dfs(int u, int fa){
     dp[u][] = ;
     int tem1 = , tem2 = ;
     for(int i = head[u]; i + ; i = edge[i].next){
         int v = edge[i].to;
         if(v == fa) continue;
         dfs(v, u);
         dp[u][] += dp[v][];
         o[u][] |= o[v][];
         int d = dp[v][] > dp[v][] ?  : (dp[v][] == dp[v][] ? - : );
         if(d == -){
             dp[u][] += dp[v][];
             o[u][] = ;
         }else{
             dp[u][] += dp[v][d];
             o[u][] |= o[v][d];
         }
     }
 }

 int main(){
     //freopen("in.txt", "r", stdin);
     while(~scanf("%d", &n) && n){
         k = ;
         int base = ;
         get_str(buf);
         mapi.clear();
         mapi[string(buf)] = ++base;
         N = ;
         memset(head, -, sizeof head);
         for(int i = , x, y; i < n; i++){
             get_str(buf);
             if(mapi.find(string(buf)) == mapi.end()) mapi[string(buf)] = ++base, x = base;
             else x = mapi[string(buf)];
             get_str(buf);
             if(mapi.find(string(buf)) == mapi.end()) mapi[string(buf)] = ++base, y = base;
             else y = mapi[string(buf)];
             addEdge(x, y);
             addEdge(y, x);
         }
         memset(dp, , sizeof dp);
         memset(o, , sizeof o);
         dfs(, );
         int ans = -;
         bool ok = ;
         for(int i = ; i <= n; i++) for(int j = ; j <= ; j++){
             if(dp[i][j] > ans) ans = dp[i][j], ok = o[i][j];
             else if(dp[i][j] == ans) ok = ;
         }
         printf("%d %s\n", ans, ok ? "No" : "Yes");
     }
     return ;
 }