UVA 12452

来源：互联网发布：金蝶数据库修复工具编辑：程序博客网时间：2024/06/08 18:22

简单树形DP

昨天做这道题一直RE，最后在队友帮助下手写栈过了

今天再看昨天的代码，发现自己确实写搓了，在每次dfs中都要开10000的数组不爆才怪.....换种写法就可以了

代码能力太渣没办法，继续加油！

#include<iostream>#include<cstring>#include<cstdio>#include<algorithm>#include<cmath>#include<stack>#include<queue>#include<vector>#include<map>#include<ctime>#include<set>#include<string>#define N 20010using namespace std;struct Edge{    int v,next;}edge[N*2];int head[N];int n,cnt;int dp[N][2];void init(){    memset(head,-1,sizeof(head));    memset(dp,0,sizeof(dp));    cnt=0;}void addedge(int u,int v){    edge[cnt].v=v;    edge[cnt].next=head[u];    head[u]=cnt++;    edge[cnt].v=u;    edge[cnt].next=head[v];    head[v]=cnt++;}void dfs(int u,int fa){    int sum=0;    int ans1=0,ans2=0;    int a[2],j=0;    a[0]=a[1]=1000000000;    for(int i=head[u];i!=-1;i=edge[i].next){        int v=edge[i].v;        if(v==fa)continue;        sum++;        dfs(v,u);        ans1+=dp[v][0];        ans2+=dp[v][1];        if(a[0]>dp[v][0]-dp[v][1]){            a[1]=a[0];            a[0]=dp[v][0]-dp[v][1];        }        else if(a[1]>dp[v][0]-dp[v][1]) a[1]=dp[v][0]-dp[v][1];    }    if(sum==0){        dp[u][0]=0;        dp[u][1]=100;        return ;    }    dp[u][0]=ans2;    dp[u][0]=min(dp[u][0],ans1+500);     //all cover    dp[u][0]=min(dp[u][0],ans2+a[0]+100);  //cover 1    if(sum>1)        dp[u][0]=min(dp[u][0],ans2+a[0]+a[1]+175); //cover 2    if(fa==-1)return;    dp[u][1]=ans2+100;    dp[u][1]=min(dp[u][1],ans1+500);    //all cover    dp[u][1]=min(dp[u][1],ans2+a[0]+175);}int main(){    int t,T,u,v,i;    scanf("%d",&T);    for(t=1;t<=T;t++){        scanf("%d",&n);        init();        for(i=0;i<n-1;i++){            scanf("%d %d",&u,&v);            addedge(u,v);        }        dfs(0,-1);        printf("$%d\n",dp[0][0]);    }    return 0;}

手写栈的版本

//#pragma comment(linker,"/STACK:1024000000,1024000000")#include <cstdio>#include <cstring>#include <algorithm>#include<stack>#define N 100010using namespace std;struct Edge{    int v,next;}edge[N*2];int head[N];int n,cnt;int dp[N][2];void init(){    memset(head,-1,sizeof(head));    memset(dp,0,sizeof(dp));    cnt=0;}void addedge(int u,int v){    edge[cnt].v=v;    edge[cnt].next=head[u];    head[u]=cnt++;    edge[cnt].v=u;    edge[cnt].next=head[v];    head[v]=cnt++;}void dfs(){    stack<pair<int, int> > sta;    sta.push(make_pair(0, -1));                //*******    bool vis[N];    memset(vis,0,sizeof(vis));    while (!sta.empty()){                         //*******        int u = sta.top().first, fa = sta.top().second;      //*******                if(vis[u]==0){                              //*******            for(int i=head[u];i!=-1;i=edge[i].next){                int v=edge[i].v;                if(v==fa)continue;                sta.push(make_pair(v, u));     //*******            }            vis[u]=1;                         //*******        }        if (u != sta.top().first)           //*******            continue;        sta.pop();                         //*******        int sum=0;        int ans1=0,ans2=0;        for(int i=head[u];i!=-1;i=edge[i].next){            int v=edge[i].v;            if(v==fa)continue;            sum++;            ans1+=dp[v][0];            ans2+=dp[v][1];        }        if(sum==0){            dp[u][0]=0;            dp[u][1]=100;            continue ;        }        dp[u][0]=ans2;        if(sum==1) dp[u][0]=min(dp[u][0],ans1+100);        else if(sum==2) dp[u][0]=min(dp[u][0],ans1+175);        else dp[u][0]=min(dp[u][0],ans1+500);     //all cover        int a[N],j=0;        if(sum>1){            for(int i=head[u];i!=-1;i=edge[i].next){                int v=edge[i].v;                if(v==fa)continue;                a[j++]=dp[v][0]-dp[v][1];            }            sort(a,a+j);            dp[u][0]=min(dp[u][0],ans2+a[0]+100);  //cover 1            if(sum>2)                dp[u][0]=min(dp[u][0],ans2+a[0]+a[1]+175); //cover 2        }        if(fa==-1)continue;        dp[u][1]=ans2+100;        if(sum==1) dp[u][1]=min(dp[u][1],ans1+175);        else dp[u][1]=min(dp[u][1],ans1+500);    //all cover        if(sum>1){            dp[u][1]=min(dp[u][1],ans2+a[0]+175);        }    }}int main(){    int t,T,u,v,i;    scanf("%d",&T);    for(t=1;t<=T;t++){        scanf("%d",&n);        init();        for(i=0;i<n-1;i++){            scanf("%d %d",&u,&v);            addedge(u,v);        }        dfs();        printf("$%d\n",dp[0][0]);    }    return 0;}