HDU - 1054 Strategic Game

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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;}

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