pku3659 Cell Phone Network

http://poj.org/problem?id=3659

树状DP,树的最小点覆盖

 #include <stdio.h>
 #include <vector>
 #define N 10010

 using namespace std;

 vector<int> a[N];
 int mark[N], dp[N][];
 const int inf = ;

 int min(int x, int y)
 {
     return x<y? x: y;
 }

 int limit_inf(int x)
 {
     return x>inf? inf: x;
 }

 int f(int x, vector<int> b)
 {
     int i, j, k, sum1, min1;

     //leaf
     if(b.size() == )
     {
         dp[x][] = ;
         dp[x][] = inf;
         dp[x][] = ;
         return ;
     }

     //
     sum1 = ;
     for(i=; i<b.size(); i++)
     {
         sum1 += dp[b[i]][];
     }
     dp[x][] = limit_inf(sum1);

     //
     min1 = inf;
     for(i=; i<b.size(); i++)
     {
         sum1 = dp[b[i]][];
         for(j=; j<b.size(); j++)
         {
             if(j != i)
             {
                 sum1 += min(dp[b[j]][], dp[b[j]][]);
             }
         }
         min1 = min(min1, sum1);
     }
     dp[x][] = limit_inf(min1);

     //
     sum1 = ;
     for(i=; i<b.size(); i++)
     {
         sum1 += min(dp[b[i]][], min(dp[b[i]][], dp[b[i]][]));
     }
     sum1 += ;
     dp[x][] = limit_inf(sum1);
     return ;
 }

 int dfs(int x)
 {
     int i, j;
     vector<int> b;
     b.clear();
     //printf("(%d: ", x);
     for(i=; i<a[x].size(); i++)
     {
         j = a[x][i];
         if(mark[j] == )
         {
             b.push_back(j);
             mark[j] = ;
             dfs(j);
         }
     }
     f(x, b);
     //printf("[%d,%d,%d]", dp[x][0], dp[x][1], dp[x][2]);
     //printf(" ) ");
     return ;
 }

 int main()
 {
     int n, i, x, y;
     while(~scanf("%d", &n))
     {
         for(i=; i<=n; i++)
         {
             //dp[i][0] = dp[i][1] = dp[1][2] = inf;
             mark[i] = ;
             a[i].clear();
         }
         for(i=; i<=n-; i++)
         {
             scanf("%d%d", &x, &y);
             a[x].push_back(y);
             a[y].push_back(x);
         }
         mark[] = ;
         dfs();
         printf("%d\n", min(dp[][], dp[][]));
         if(dp[][] == inf)
         {
             dp[][] = -;
         }
         //printf("\n");
         //for(i=1; i<=n; i++)
         //{
         //   printf("%5d %5d %5d\n", dp[i][0], dp[i][1], dp[i][2]);
         //}
     }
     return ;
 }