Poj 1947 Rebuilding Roads

树dp+背包

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考虑是否加入子树k
时间复杂度O(n3)

#include<cstdio>#include<vector>#include<algorithm>#include<cstring>using namespace std;const int INF = 0x3f3f3f3f;const int maxn = 200;vector<int> edge[maxn];int dp[maxn][maxn];void dfs(int st,int fa){    dp[st][1] = 0;    for(vector<int>::iterator it = edge[st].begin();it!=edge[st].end();it++){        int x = *it;         if(x == fa) continue;        dfs(x,st);        for(int v = maxn-1;v >= 1;v--){            dp[st][v]++;            for(int k=1;k<v;k++){                dp[st][v] = min(dp[st][v-k] + dp[x][k],dp[st][v]);            }        }    } }int anser(int n,int p){    int ret = dp[1][p];    for(int i=2;i<=n;i++){        ret = min(ret,dp[i][p]+1);    }    return ret;}int main(){    int n,d;    while(~scanf("%d %d",&n,&d)){        memset(dp,0x3f,sizeof(dp));        int l,r;        for(int i=1;i<n;i++){            scanf("%d %d",&l,&r);            edge[l].push_back(r);            edge[r].push_back(l);        }        dfs(1,0);        printf("%d\n",anser(n,d));    }    return 0;}