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][3];
const int inf = 12345678;

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() == 0)
    {
        dp[x][0] = 0;
        dp[x][1] = inf;
        dp[x][2] = 1;
        return 0;
    }
    
    //0
    sum1 = 0;
    for(i=0; i<b.size(); i++)
    {
        sum1 += dp[b[i]][1];
    }
    dp[x][0] = limit_inf(sum1);

    //1
    min1 = inf;
    for(i=0; i<b.size(); i++)
    {
        sum1 = dp[b[i]][2];
        for(j=0; j<b.size(); j++)
        {
            if(j != i)
            {
                sum1 += min(dp[b[j]][1], dp[b[j]][2]);
            }
        }
        min1 = min(min1, sum1);
    }
    dp[x][1] = limit_inf(min1);

    //2
    sum1 = 0;
    for(i=0; i<b.size(); i++)
    {
        sum1 += min(dp[b[i]][0], min(dp[b[i]][1], dp[b[i]][2]));
    }
    sum1 += 1;
    dp[x][2] = limit_inf(sum1);
    return 0;
}

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

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