P1508 - [蓝桥杯2020初赛] 门牌制作 - New Online Judge

#include<bits/stdc++.h>
using namespace std;

int main()
{
	int res = 0;
	for(int i = 1; i <= 2020; i++)
	{
		int num = i;
		while(num)
		{
			if(num % 10 == 2) res++;
			num/=10;
		}
	}
	cout<<res;
	return 0;
}

624

P1509 - [蓝桥杯2020初赛] 既约分数 - New Online Judge

#include<bits/stdc++.h>

using namespace std;
int gcd(int x,int y)
{
	//辗转相除
	/*
		x / y == n ... m
		y / m == n2 ... m2
		 
	*/ 
	
	while(x % y)
	{
		int z = x % y;
		x = y;
		y = z;
	}
	
	//别忘记return y
	return y; 
}
int main()
{
	long long res = 0;
	for(int i = 1;i <= 2020; i++)
	{
		for(int j = 1; j<= 2020; j++)
		{
			if(gcd(i,j)==1) res++; 
		}
	}
	cout<<res;
	return 0;
}

2481215

P1514 - [蓝桥杯2020初赛] 约数个数 - New Online Judge

#include<iostream>
#include<cstring>
#include<algorithm>

using namespace std;

int main()
{
	
	int n = 1200000;
	long long res = 0;
	for(int i = 1;i <= n; i++)
	{
		if(n % i == 0) res++;
	}
	cout<<res;
	return 0;
}

96

P1550 - [蓝桥杯2021初赛] 卡片 - New Online Judge

#include<iostream>
#include<cstring>
#include<algorithm>

using namespace std;

int main()
{
	
	int a[10];
	for(int i = 0;i<=9;i++)a[i] = 2021;// 
	
	bool flag = false;
	 int i = 1;//从1开始
	while(!flag)
	{
		int num = i;
		while(num)
		{
			int k = num % 10;
			if(a[k]<=0) 
			{
				flag = true;
			}
			a[k]--;
		
			num /= 10;
		}
		if(flag)
		{
			cout<<i - 1;//当前不能拼接，返回上一个可以拼接的数字 
			break; 
		} 
		i++;
	}
	
	 
	return 0;
}

3181