第十四届蓝桥杯三月真题刷题训练——第 9 天（3.12）

[华年的小年华]

第一题：

朴素版

#include <iostream>

using namespace std;

const int N = 100010;

int cnt;

bool check(int x)
{
    for (int i = 2; i <= x / i; i ++ ) 
        if (x % i == 0) 
            return false;
    return true;
}

int main()
{
    for (int i = 2; ; i ++ ) 
       {
           if (check(i)) cnt ++ ;
        if (cnt == 100002) 
        {
            cout << i << endl;
            return 0;    
        }
    }
    return 0;
}

筛：

#include <iostream>

using namespace std;

const int N = 1e6;
int primes[N], cnt;
bool st[N];

void get_primes(int n)
{
    for (int i = 2; i <= n; i ++ ) 
    {
        if (!st[i]) primes[cnt ++ ] = i;
        for (int j = 0; primes[j] <= n / i; j ++ ) 
        {
            st[primes[j] * i] = true;
            if (i % primes[j] == 0) break;
        }
    }
}

int main()
{   
    get_primes(N - 1);
    int res = 0;
    for (int i = 2; ; i ++ ) 
    {
        if (!st[i]) res ++ ;
        if (res == 100002) 
        {
            cout << i << endl;
            return 0;
        }
    }
    return 0;
}

第二题：全排列函数

 

#include <iostream>
#include <algorithm>

using namespace std;

const int N = 15;

int num[N];
int ans;

bool check()
{
    for (int i = 0; i < 9; i ++ ) 
        if (abs(num[i + 1] - num[i]) == 1) return false;

    return true;
}

int main()
{
    for (int i = 0; i < 10; i ++ ) num[i] = i + 1;
    do {
        if (check()) ans ++ ;
    }while (next_permutation(num, num + 10));

    cout << ans << endl;
}

第三题：双指针

#include <bits/stdc++.h>

using namespace std;

const int N = 100010;

struct ret{
    int id;
    int ts;
}p[N];

int n, d, k;
int cnt[N];
bool st[N];

int main()
{
    scanf("%d%d%d", &n, &d, &k);
    for (int i = 0; i < n; i ++ ) cin >> p[i].ts >> p[i].id;

    sort(p, p + n, [&](ret a, ret b){
        return a.id < b.id;
    });

    for (int i = 0, j = 0; i < n; i ++ ) 
    {
        auto id = p[i].id;
        cnt[id] ++ ;

        while (j < i && p[i].ts - p[j].ts >= d)
        {
            cnt[p[j].id] -- ;
            j ++ ;
        }
        if (cnt[id] >= k) st[id] = true;
    }

    for (int i = 0; i < N; i ++ )
        if (st[i]) cout << i << endl;

    return 0;
}