11.15

https://codeforces.com/gym/102411/problem/M

ICPC 2019-2020 North-Western Russia Regional Contest

//A
#include<iostream>
#include<cstdio>
using namespace std;
int main(){
    int a,b,n;
    int x,y,ans=0;
    scanf("%d%d%d",&a,&b,&n);
    x=(n-b)%(b-a);
    y=(n-b)/(b-a);
    if(x)x=3;
    else x=1;
    ans=2*y+x;
    printf("%d
",ans);
    return 0;
}

//E
#include<iostream>
#include<cstdio>
#define maxn 200010
using namespace std;
int n,m,dep[maxn],head[maxn],num,a[maxn],fa[maxn];
struct node{
    int to,pre;
}e[maxn*2];
void Insert(int from,int to){
    e[++num].to=to;
    e[num].pre=head[from];
    head[from]=num;
}
void dfs(int now,int father){
    dep[now]=dep[father]+1;
    fa[now]=father;
    for(int i=head[now];i;i=e[i].pre){
        int to=e[i].to;
        if(to==father)continue;
        dfs(to,now);
    }
}
int main(){
    freopen("Cola.txt","r",stdin); 
    scanf("%d%d",&n,&m);
    int x,y;
    for(int i=1;i<n;i++){
        scanf("%d%d",&x,&y);
        Insert(x,y);
        Insert(y,x);
    }
    for(int i=1;i<=m;i++)scanf("%d",&a[i]);
    if(m==1){
        puts("YES");
        printf("%d
",a[1]);
        return 0;
    }
    dfs(a[1],0);
    int now=a[2];
    for(int i=3;i<=m;i++){
        if(dep[a[i]]>dep[now])now=a[i];
    }
    int depx=(dep[a[1]]+dep[now])/2;
    if((dep[now]-dep[a[1]])%2!=0){
        puts("NO");
        return 0;
    }
    int depnow=dep[now];
    while(depnow>depx){
        now=fa[now];
        depnow=dep[now];
    }
    dfs(now,0);
    int dis=dep[a[1]]-1;
    for(int i=2;i<=m;i++){
        if(dep[a[i]]-1!=dis){
            puts("NO");
            return 0;
        }
    }
    puts("YES");
    printf("%d
",now);
    return 0;
}

//M
//充满魔性的a了一发
#include<iostream>
#include<cstdio>
#include<cstring>
#define maxn 2010
#define mod1 2353733
#define mod2 12377
using namespace std;
int Case,n,a[maxn],b[maxn];
int tim[10000010];
long long ans;
int Hash(int x){
    return (1LL*x*107%mod1+1LL*x*23%mod1+1LL*x*37%mod1)%mod1;
}
int main(){
    scanf("%d",&Case);
    while(Case--){
        memset(tim,0,sizeof(tim));
        ans=0;
        scanf("%d",&n);
        for(int i=1;i<=n;i++){
            scanf("%d",&a[i]);
            b[i]=a[i]*2;
        }
        for(int i=2;i<n;i++){//ö¾ÙÖмäÊýµÄλÖà 
            int hs=Hash(a[i-1]);
            tim[hs]++;
            for(int j=i+1;j<=n;j++){
                if(a[j]<b[i]){
                    int hsnow=Hash(b[i]-a[j]);
                    ans=ans+tim[hsnow];
                }
            }
        }
        cout<<ans<<endl;
    }
    return 0;
}