Codeforces Round #269 (Div. 2) A B C

先说C

题目链接：http://codeforces.com/problemset/problem/471/C

题目意思：有 n 张卡，问能做成多少种不同楼层（floor）的 house。注意这 n 张卡都要用光。每层 floor 都由一定的 room 构成，每两个相邻 room 规定要有一个公共的ceiling。规定从上到下看，每层 floor 的 room 的数量呈递增的形式排布。

这样的东西一般就是看图，先自己从小数開始推算找规律 能够发现第i层须要(3*i+2)个，那么前i层总的最少须要就是等差数列求和得(3*i+1)*i/2。  由于不能剩余。那么n-(3*i+1)*i/2必须能被3整除。那么从1到(3*i+1)*i/2<=n遍历一下即可 n=10^12  所以O(1e6)时间还是够的

//#pragma comment(linker, "/STACK:102400000,102400000")
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <iostream>
#include <iomanip>
#include <cmath>
#include <map>
#include <set>
#include <queue>
using namespace std;

#define ls(rt) rt*2
#define rs(rt) rt*2+1
#define ll long long
#define ull unsigned long long
#define rep(i,s,e) for(int i=s;i<e;i++)
#define repe(i,s,e) for(int i=s;i<=e;i++)
#define CL(a,b) memset(a,b,sizeof(a))
#define IN(s) freopen(s,"r",stdin)
#define OUT(s) freopen(s,"w",stdout)
const ll ll_INF = ((ull)(-1))>>1;
const double EPS = 1e-8;
const double pi = acos(-1.0);
const int INF = 100000000;

int main()
{
    ll n;
    while(~scanf("%I64d",&n))
    {
        ll ans=0,tmp;
        for(ll i=1;(tmp=(3*i+1)*i/2)<=n;i++)
        {
            if( ( n-tmp )%3 == 0)
                ans++;
        }
        printf("%I64d
",ans);
    }
    return 0;
}

B,  首先能不能出现三种以上的排列，写代码时用了类似离散化的写法，能的话  就随便改两个数的次序就能凑够3种

//#pragma comment(linker, "/STACK:102400000,102400000")
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <iostream>
#include <iomanip>
#include <cmath>
#include <map>
#include <set>
#include <queue>
using namespace std;

#define ls(rt) rt*2
#define rs(rt) rt*2+1
#define ll long long
#define ull unsigned long long
#define rep(i,s,e) for(int i=s;i<e;i++)
#define repe(i,s,e) for(int i=s;i<=e;i++)
#define CL(a,b) memset(a,b,sizeof(a))
#define IN(s) freopen(s,"r",stdin)
#define OUT(s) freopen(s,"w",stdout)
const ll ll_INF = ((ull)(-1))>>1;
const double EPS = 1e-8;
const double pi = acos(-1.0);
const int INF = 100000000;

const int MAXN = 2000+20;
struct Node{
    int id,v;
}p[MAXN];
int n;
bool cmp(Node a, Node b)
{
    return a.v<b.v;
}

void print()
{
    printf("%d",p[1].id);
    for(int i=2;i<=n;i++)
        printf(" %d",p[i].id);
    putchar('
');
}

void SW(Node &a, Node &b)
{
    Node tmp;
    tmp=a;
    a=b;
    b=tmp;
}

int main()
{

    while(~scanf("%d",&n))
    {
        for(int i=1;i<=n;i++)
        {
            scanf("%d",&p[i].v);
            p[i].id=i;
        }
        sort(p+1,p+n+1,cmp);
        p[n+1].v=-1;
        int tmp=1,pre=p[1].v;
        ll cnt=1;
        int flag=0;
        for(int i=2;i<=n+1;i++)
            if(pre!=p[i].v)
            {
                if(tmp>=3){flag=1;break;}
                cnt*=tmp;
                if(cnt>=3){flag=1;break;}
                tmp=1;
                pre=p[i].v;
            }
            else
            {
                tmp++;
            }
        if(!flag)puts("NO");
        else
        {
            puts("YES");
            print();
            int pr=p[1].v,tmp=1;
            int cnt=1;
            for(int i=2;i<=n+1;i++)///
                if(pr!=p[i].v)
                {
                    if(tmp==2)
                    {
                        SW(p[i-1],p[i-2]);
                        if(cnt<3)print(),cnt++;;

                    }
                    if(tmp >= 3)
                    {
                        SW(p[i-1],p[i-2]);
                        if(cnt<3) print(),cnt++;
                        //cnt++;
                        SW(p[i-1],p[i-3]);
                        if(cnt<3)print(),cnt++;
                        //cnt++;
                    }
                    if(cnt >=3)break;
                    tmp=1;
                    pr=p[i].v;
                }
                else
                {
                    tmp++;
                }
        }
    }
    return 0;
}

A  水  只是由于flag少写了一个 WA了一次

//#pragma comment(linker, "/STACK:102400000,102400000")
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <iostream>
#include <iomanip>
#include <cmath>
#include <map>
#include <set>
#include <queue>
using namespace std;

#define ls(rt) rt*2
#define rs(rt) rt*2+1
#define ll long long
#define ull unsigned long long
#define rep(i,s,e) for(int i=s;i<e;i++)
#define repe(i,s,e) for(int i=s;i<=e;i++)
#define CL(a,b) memset(a,b,sizeof(a))
#define IN(s) freopen(s,"r",stdin)
#define OUT(s) freopen(s,"w",stdout)
const ll ll_INF = ((ull)(-1))>>1;
const double EPS = 1e-8;
const double pi = acos(-1.0);
const int INF = 100000000;

int len[10],vis[12];

int main()
{
    while(~scanf("%d%d%d%d%d%d",len,len+1,len+2,len+3,len+4,len+5))
    {
        int ans=0;
        CL(vis,0);
        sort(len,len+6);
        int cnt=0,flag=0;
        for(int i=0;i<6;i++)
        {
            vis[len[i]]++;
            if(vis[len[i]] == 4)cnt=i,flag=1;
        }
        if(vis[len[cnt]] == 5)
        {
            puts("Bear");
            continue;
        }
        if(vis[len[cnt]] == 6)
        {
            puts("Elephant");
            continue;
        }
        int last=-1,ff=0;
        for(int i=0;i<6;i++)
            if(i!=cnt)
            {
                if(vis[len[i]] == 2)ff=1;
                if(last==-1){len[0]=len[i];last=1;}
                else  len[5]=len[i];
            }
        if(ff && flag)
        {
            puts("Elephant");
            continue;
        }
        if(len[0]!=len[5] && flag)
        {
            puts("Bear");
            continue;
        }
        if(len[0]==len[5] && flag)
        {
            puts("Elephant");
            continue;
        }
        puts("Alien");
    }
    return 0;
}