HDU - 1054 Strategic Game

题意：给定一棵树，选择最小的节点，使得每个没有被选中的节点至少和一个已选节点相邻

思路：简单的树形DP

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
using namespace std;
const int MAXN = 1600;

vector<int> g[MAXN];
int dp[MAXN][2],vis[MAXN];
int n,num,x;

void dfs(int r){
    if (vis[r])
        return;
    vis[r] = 1;
    dp[r][0] = 0;
    dp[r][1] = 1;
    if (g[r].size() == 0)
        return;
    for (int i = 0; i < g[r].size(); i++){
        int j = g[r][i];
        if (vis[j])
            continue;
        dfs(j);
        dp[r][0] += dp[j][1];
        dp[r][1] += min(dp[j][0],dp[j][1]);
    }
}

int main(){
    while (scanf("%d",&n) != EOF){
        for (int i = 0; i <= n; i++)
            g[i].clear();
        for (int i = 0; i < n; i++){
            scanf("%d:(%d)",&x,&num);
            for (int j = 0; j < num; j++){
                int y;
                scanf("%d",&y);
                g[x].push_back(y);
                g[y].push_back(x);
            }
        }
        memset(vis,0,sizeof(vis));
        dfs(0);
        printf("%d\n",min(dp[0][0],dp[0][1]));
    }
    return 0;
}