蓝桥杯打卡第9天（冲，冲，冲）

[木杉]

1.找素数

#include <iostream>
using namespace std;
bool check(int x)
{
  for(int j = 2; j * j <= x; j ++)
  {
    if(x % j == 0)
      return false;
  }
  return true;
}
int main()
{
  int num = 0;
  for(int i = 2; ; i ++)
  {
    if(check(i))
      num ++;
    if(num == 100002)
    {
      cout << i << endl;
      break;
    }
  }
  return 0;
}

2.图书排列

#include <iostream>
using namespace std;
int book[15],sum=0;
bool tag[11];
void dfs(int step){
  if(step>=3&&abs(book[step-1]-book[step-2])<=1) return;
  if(step==11) {
    sum++;
    return;
  }
  for(int i=1;i<=10;i++){
    if(tag[i]==false){
      book[step]=i;
      tag[i]=true;
      dfs(step+1);
      tag[i]=false;
   }
  }
}
int main()
{
  dfs(1);
  cout<<sum;
  return 0;
}

3.日志统计

#include<cstdio>
#include<algorithm>
using namespace std;
int n,d,k;
int nowlike[100005];
struct node{
    int ts;
    int id;
};
node arr[100005];
bool ishot[100005];
bool cmp(node x,node y)
{
    return x.ts<y.ts;
}
int main()
{
    scanf("%d%d%d",&n,&d,&k);
    for(int i=1;i<=n;i++)
        scanf("%d%d",&arr[i].ts,&arr[i].id);
    sort(arr+1,arr+1+n,cmp);
    int l = 1;
    for(int i=1;i<=n;i++)
    {  
            nowlike[arr[i].id]++;
        while(arr[i].ts >= arr[l].ts + d) nowlike[arr[l++].id]--;
        if(nowlike[arr[i].id]>=k) ishot[arr[i].id] = true;
    }
    for(int i=0;i<=100005;i++)
        if(ishot[i])
            printf("%d\n",i);
    return 0;
}

4.杨辉三角形

#include <iostream>
using namespace std;
typedef long long LL;
LL n;
LL C(int x,int k){
  LL ans=1;
  for(int i=x,j=1;j<=k;i--,j++){
    ans=ans*i/j;
    if(ans>n)return ans;
  }
  return ans;
}
bool check(int x){
  LL l=2*x,r=max(n,l);
  while(l<r){
    int mid=l+r>>1;
    if(C(mid,x)>=n)r=mid;
    else l=mid+1;
  }
  if(C(r,x)!=n)return false;
  cout<<(LL)(r+1)*r/2+x+1<<endl;
  return true;
}
int main(){
  cin>>n;
  for(int t=17;;t--){
    if(check(t))break;
  }
  return 0;
}