hdu 4781 Beautiful Soup 构造

并不是很难的一个构造，我在比赛的时候把题目读错了，补题的时候想得比较粗糙，迟迟没过这题，之后想法慢慢细致起来，还是将这题过了。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#define REP(i,a,b) for(int i=a;i<=b;i++)
#define MS0(a) memset(a,0,sizeof(a))

using namespace std;

typedef long long ll;
const int maxn=1000100;
const int INF=1e9+10;

int n,m;
struct Edge
{
    int u,v,w;
    friend bool operator<(Edge A,Edge B)
    {
        return A.w<B.w;
    }
};Edge ans[maxn];int ansn;
int flag;
int cur;
int e[120][120];
bool vis[120][120];
bool used[maxn];

void putA()
{
    REP(i,1,n) REP(j,1,n) e[i][j]=i==j?0:INF;
    ansn=0;
    MS0(vis);MS0(used);
    int sum=0;
    int cur=4;
    int finish=0;
    REP(i,1,n-1){
        if(cur>m){
            finish=1;
            cur=3;
        }
        int j=i+1;
        e[i][j]=cur;
        vis[i][j]=vis[j][i]=1;
        used[cur]=1;
        ans[++ansn]={i,j,cur};
        sum+=cur;
        if(finish) cur+=3;
        else if(i%2) cur++;
        else cur+=2;
    }
    REP(i,1,m){
        if(used[i]) continue;
        if((sum+i)%3==0){
            used[i]=1;
            vis[n][1]=vis[1][n]=1;
            e[n][1]=i;
            ans[++ansn]={n,1,i};
            sum+=i;
            break;
        }
    }
    if(sum%3) flag=-1;
}

void floyd()
{
    REP(k,1,n){
        REP(i,1,n){
            //if(k==i) continue;
            REP(j,1,n){
                //if(j==k||j==i) continue;
                if(e[i][k]+e[k][j]<e[i][j]) e[i][j]=e[i][k]+e[k][j];
            }
        }
    }
}

void putB()
{
    //REP(i,1,n) if(e[i][i%n+1]==INF) cout<<"i="<<i<<" j="<<i%n+1<<" e="<<e[i][i%n+1]<<endl;
    floyd();
    /*
    REP(i,1,n) REP(j,1,n){
        if(e[i][j]==INF) cout<<"i="<<i<<"j="<<j<<" e="<<e[i][j]<<endl;
    }
    */
    REP(i,1,m){
        if(used[i]) continue;
        int tag=0;
        REP(j,1,n){
            REP(k,1,n){
                //if(i==6&&j!=k) cout<<e[j][k]<<" "<<j<<" "<<k<<" "<<vis[j][k]<<endl;
                if(j==k||vis[j][k]||e[j][k]%3!=i%3) continue;
                used[i]=1;
                vis[j][k]=vis[k][j]=1;
                ans[++ansn]={j,k,i};
                tag=1;break;
            }
            if(tag) break;
        }
    }
    //REP(i,1,m) cout<<used[i]<<" ";cout<<endl;
    REP(i,1,m) if(!used[i]) flag=-1;
}

int main()
{
    #ifndef ONLINE_JUDGE
        freopen("in.txt","r",stdin);
    #endif // ONLINE_JUDGE
    int T;cin>>T;int casen=1;
    while(T--){
        scanf("%d%d",&n,&m);
        flag=0;
        putA();
        if(~flag) putB();
        printf("Case #%d:
",casen++);
        if(flag==-1) puts("-1");
        else{
            sort(ans+1,ans+ansn+1);
            REP(i,1,ansn) printf("%d %d %d
",ans[i].u,ans[i].v,ans[i].w);
        }
    }
    return 0;
}
/**
7
6 8
5 8
6 9
6 8
10 13
10 14
7 11
4
10 13
10 14
80 83
80 974

*/