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  • Codeforces Round #670 (Div. 2)

    A

    #include "bits/stdc++.h"
    using namespace std;
    #define all(v) (v).begin(), (v).end()
    #define io ios::sync_with_stdio(0)
    #define rep(i, a, b) for (int i = a; i <= b; i++)
    #define rson rt << 1 | 1, mid + 1, r
    #define lson rt << 1, l, mid
    #define lll __int128
    #define lowbit(i) ((-i) & (i))
    #define pii pair<int, int>
    #define fi first
    #define se second
    #define mp make_pair
    #define pb push_back
    
    
    template<class T>void read(T &x)
    {
        x=0;
        int f=0;
        char ch=getchar();
        while(ch<'0'||ch>'9')
        {
            f|=(ch=='-');
            ch=getchar();
        }
        while(ch>='0'&&ch<='9')
        {
            x=(x<<1)+(x<<3)+(ch^48);
            ch=getchar();
        }
        x=f?-x:x;
        return;
    }
    
    #define ull unsigned long long
    #define eps 1e-12
    #define sc(x) scanf("%lld", &(x))
    #define mem(a,b) memset(a,b,sizeof(a))
    #define endl "
    "
    #define inf 0x3f3f3f3f
    #define ll long long
    const int mod = 1e9+7;
    const int maxn=5e5+10;
    
    
    int a[maxn];
    
    void work()
    {
        mem(a,0);
        int n;
        cin>>n;
        rep(i,1,n)
        {
            int now;
            cin>>now;
            a[now]++;
        }
        int ans=0;
        rep(i,0,100)
        {
            if(a[i]==0)
            {
                ans+=i;
                break;
            }
            a[i]--;
        }
        rep(i,0,100)
        {
            if(a[i]==0) {ans+=i;break;}
        }
        cout<<ans<<endl;
    }
    
    signed main()
    {
        int t;
        cin>>t;
        while(t--)
        work();
    }
    
    

    B

    当ans为正数时,正数取前5大,负数取前5小,枚举取答案
    负数时, 负数取前五大,取答案
    有0时ans最小为0

    #include "bits/stdc++.h"
    using namespace std;
    #define all(v) (v).begin(), (v).end()
    #define io ios::sync_with_stdio(0)
    #define rep(i, a, b) for (int i = a; i <= b; i++)
    #define rson rt << 1 | 1, mid + 1, r
    #define lson rt << 1, l, mid
    #define lll __int128
    #define lowbit(i) ((-i) & (i))
    #define pii pair<int, int>
    #define fi first
    #define se second
    #define mp make_pair
    #define pb push_back
    
    
    template<class T>void read(T &x)
    {
        x=0;
        int f=0;
        char ch=getchar();
        while(ch<'0'||ch>'9')
        {
            f|=(ch=='-');
            ch=getchar();
        }
        while(ch>='0'&&ch<='9')
        {
            x=(x<<1)+(x<<3)+(ch^48);
            ch=getchar();
        }
        x=f?-x:x;
        return;
    }
    
    #define ull unsigned long long
    #define eps 1e-12
    #define sc(x) scanf("%lld", &(x))
    #define mem(a,b) memset(a,b,sizeof(a))
    #define endl "
    "
    #define inf 0x3f3f3f3f
    #define ll long long
    #define int long long
    const int mod = 1e9+7;
    const int maxn=5e5+10;
    
    
    int a[maxn];
    int b[maxn];
    int c[maxn];
    
    int ans;
    
    void dfs(int dep,int st,int ed,int now)
    {
    //    cout<<st<<" "<<ed<<endl;
        if(dep==5)
        {
            ans=max(ans,now);
            return ;
        }
        rep(i,st,ed)
        {
            dfs(dep+1,i+1,ed,now*c[i]);
            dfs(dep,i+1,ed,now);
        }
        return ;
    }
    
    int cmp(int a,int b)
    {
        return a>b;
    }
    
    void work()
    {
        int la=0,lb=0,n;
        ans=-1e18;
        cin>>n;
        rep(i,1,n)
        {
            int now;
            cin>>now;
            if(now>0) a[++la]=now;
            else if(now<0) b[++lb]=now;
            else if(now==0) ans=0;
        }
        sort(a+1,a+1+la,cmp);
        sort(b+1,b+1+lb);
        int e1=min(la,1ll*5);
        int e2=min(lb,1ll*5);
        int l=0;
    //    rep(i,1,e2) cout<<b[i]<<endl;
        rep(i,1,e1) c[++l]=a[i];
        rep(i,1,e2)
        {
            c[++l]=b[i];
    //        cout<<b[i]<<" "<<c[l]<<endl;
        }
    //    rep(i,1,l) cout<<c[i]<<endl;
        if(l>=5)
          dfs(0,1,l,1);
    
        sort(a+1,a+1+la,cmp);
        sort(b+1,b+1+lb,cmp);
        e1=min(la,1ll*5);
        e2=min(lb,1ll*5);
        l=0;
    //    rep(i,1,e2) cout<<b[i]<<endl;
        rep(i,1,e1) c[++l]=a[i];
        rep(i,1,e2)
        {
            c[++l]=b[i];
    //        cout<<b[i]<<" "<<c[l]<<endl;
        }
    //    rep(i,1,l) cout<<c[i]<<endl;
        if(l>=5)
          dfs(0,1,l,1);
    
        cout<<ans<<endl;
    }
    
    signed main()
    {
        int t;
        cin>>t;
        while(t--)
        work();
    }
    
    

    C

    树的重心最多有 2 个且相邻
    取一个重心上不是另一个重心相连的子树, 破坏掉连到另一个重心上即可

    #include<cstdio>
    #include<algorithm>
    #include<cstring>
    #include<iostream>
    using namespace std;
    //ÇóÊ÷µÄÖØÐÄ
    const int maxn=5e5+5;
    struct node
    {
        int to,nex;
    } tr[maxn*4];
    int n,ans;
    int max_part[maxn];
    int sizx[maxn],cnt;
    int head[maxn];
    int f[maxn];
    void add(int u,int v)
    {
        tr[cnt].to=v;
        tr[cnt].nex=head[u];
        head[u]=cnt++;
    }
    void dfs(int u,int fa)
    {
        f[u]=fa;
        sizx[u]=1;
        max_part[u]=0;
        for(int i=head[u]; ~i; i=tr[i].nex)
        {
            int v=tr[i].to;
            if(v==fa)
            {
                continue;
            }
            dfs(v,u);
            sizx[u]+=sizx[v];
            max_part[u]=max(max_part[u],sizx[v]);
        }
        max_part[u]=max(max_part[u],n-sizx[u]);
        ans=min(max_part[u],ans);
    }
    
    int kk=0,ansv=0;
    void dfs1(int u,int fa)
    {
        if(kk) return ;
        for(int i=head[u]; ~i; i=tr[i].nex)
        {
            int v=tr[i].to;
            if(v==fa) continue;
            if(sizx[v]==1)
            {
                ansv=v;
                kk=1;
                return ;
            }
            dfs1(v,u);
        }
    }
    int main()
    {
        int t;
        scanf("%d",&t);
        while(t--)
        {
            for(int i=1;i<=cnt;i++)
            {
                head[i]=-1;
                tr[i].nex=0,tr[i].to=0;
    
            }
            cnt=0;
            ans=0x3f3f3f3f3f;
            scanf("%d",&n);
            for(int i=1;i<=n;i++)
            {
                f[i]=0;
                max_part[i]=0;
                head[i]=-1;
                sizx[i]=0;
            }
            for(int i=1; i<n; i++)
            {
                int u,v;
                scanf("%d %d",&u,&v);
                add(u,v);
                add(v,u);
            }
            dfs(1,0);
            int root,minx=0x3f3f3f3f;
            int num=0;
            for(int i=1;i<=n;i++)
            {
                if(max_part[i]==ans)
                {
                    root=i;
                    break;
                }
            }
    
            int root2;
            for(int i=1;i<=n;i++)
            {
                if(max_part[i]==ans)
                    root2=i;
            }
    
            int mx=0,pos;
            for(int i=head[root];~i;i=tr[i].nex)
            {
                int v=tr[i].to;
    //            cout<<v<<endl;
                if(v!=root2)
                {
                    pos=v;
                    break;
                }
            }
    
            cout<<pos<<" "<<root<<"
    ";
            cout<<pos<<" "<<root2<<"
    ";
        }
    }
    
    

    D

    维护差分
    应为 b 是非递减, c 是非递增
    所以答案应该在 bn 和 c1 中取得
    把正差分加到 b 上, 负差分加到 c 上为最优
    记正差分的和为sum, b1 为 x, c1 为 y
    所以 x+y=a1 bn=x+sum
    所以 ans=max( x+sum, a1-x )
    且当x+sum=a1-x时取得最小值

    #include "bits/stdc++.h"
    using namespace std;
    #define all(v) (v).begin(), (v).end()
    #define io ios::sync_with_stdio(0)
    #define rep(i, a, b) for (int i = a; i <= b; i++)
    #define rson rt << 1 | 1, mid + 1, r
    #define lson rt << 1, l, mid
    #define lll __int128
    #define lowbit(i) ((-i) & (i))
    #define pii pair<int, int>
    #define fi first
    #define se second
    #define mp make_pair
    #define pb push_back
    #define int long long
    
    template<class T>void read(T &x)
    {
        x=0;
        int f=0;
        char ch=getchar();
        while(ch<'0'||ch>'9')
        {
            f|=(ch=='-');
            ch=getchar();
        }
        while(ch>='0'&&ch<='9')
        {
            x=(x<<1)+(x<<3)+(ch^48);
            ch=getchar();
        }
        x=f?-x:x;
        return;
    }
    
    #define ull unsigned long long
    #define eps 1e-12
    #define sc(x) scanf("%lld", &(x))
    #define mem(a,b) memset(a,b,sizeof(a))
    #define endl "
    "
    #define inf 0x3f3f3f3f
    #define ll long long
    #define dbug cout<<"here
    ";
    
    const int mod = 1e9+7;
    const int maxn=5e5+10;
    
    
    
    int a[maxn];
    int b[maxn];
    
    
    void work()
    {
        int n,q;
        read(n);
        rep(i,1,n) read(a[i]);
        int sum=0;
        rep(i,1,n) b[i]=a[i]-a[i-1];
        rep(i,1,n) if(b[i]>0&&i!=1) sum+=b[i];
        int x;
        x=(b[1]-sum)/2;
        int ans=max(x+sum,b[1]-x);
        printf("%lld
    ",ans);
        read(q);
        while(q--)
        {
            int l,r,d;
            read(l),read(r),read(d);
            if(l==1) b[1]+=d;
            else
            {
                if(b[l]>0&&b[l]+d<=0)
                {
                    sum-=b[l];
                    b[l]+=d;
                }
                else
                {
                    if(b[l]>0)
                    {
                        b[l]+=d;
                        sum+=d;
                    }
                    else
                    {
                        b[l]+=d;
                        if(b[l]>0) sum+=b[l];
                    }
                }
            }
            if(r!=n)
            {
                r++;
                d=-d;
                if(b[r]>0&&b[r]+d<=0)
                {
                    sum-=b[r];
                    b[r]+=d;
                }
                else
                {
                    if(b[r]>0)
                    {
                        b[r]+=d;
                        sum+=d;
                    }
                    else
                    {
                        b[r]+=d;
                        if(b[r]>0) sum+=b[r];
                    }
                }
            }
            x=(b[1]-sum)/2;
            ans=max(x+sum,b[1]-x);
            printf("%lld
    ",ans);
        }
    }
    
    signed main()
    {
    
        work();
    }
    
    

    E

    简单的想法就是枚举质数, 然后判断这个质数是否为x的质因子以及系数, 但是1E5内的质数接近1E4, 查询次数不允许.
    所以对质数进行分块, 设m为质数的个数,每次删掉 sqrt(m) 的质数,同时维护一下应该剩余数的个数res, 每次删完 sqrt(m) 之后查询 1, 看和res是否相同, 确定最小的质因数, 之后同上枚举后面的每个质数

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  • 原文地址:https://www.cnblogs.com/minun/p/13681920.html
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