Practice makes perfect!

#include<algorithm>
#include<cstdio>
#include<cstring>
using namespace std;
inline int gcd(int a,int b){
	if(b==0)
		return a;
	return gcd(b,a%b);
}
int main(){
	int n;
	scanf("%d",&n);
	int ans=0;
	for(int i=1;i<=n;++i){
		for(int j=i+1;j<=n;++j){
			for(int k=j+1;k<=n;k++){
				if(gcd(i,j)==1&&gcd(j,k)==1&&gcd(i,k)==1){
					++ans;
				}
			}
		}
	}
	printf("%d\n",ans);
	return 0;
} 

#include<algorithm>
#include<cstdio>
#include<cstring>
#define ll long long
int n,k;
int a[200007];
int ans[200007];
int main(){
	scanf("%d%d",&n,&k);
	for(int i=1;i<=n;++i){
		scanf("%d",a[i]);
	}
	std::sort(a+1,a+n+1);
	n=std::unique(a+1,a+n+1)-a-1;
	for(int i=1,j=0;i<=n;++i){
		for(;j<i&&a[i]-a[j+1]>k;++j)
			;
		ans[i]=ans[j]+1;
	}
	printf("%d\n",ans[n]);
	return 0;
} 

#include<algorithm>
#include<cstdio>
#include<cstring>
#define ll long long
int f[5007][5007];
int a[5007],b[5007];
int n;
using namespace std;
int main(){
	scanf("%d",n);
	for(int i=1;i<=n;++i){
		scanf("%d",a[i]);
	}
	for(int i=1;i<=n;++i){
		scanf("%d",b[i]);
	}
	for(int i=1;i<=n;++i){
		for(int j=1;j<=n;++j){
			f[i][j]=max(f[i][j],std::max(f[i-1][j],f[i][j-1]));
			if(a[i]==b[i]){
				f[i][j]=std::max(f[i][j],f[i-1][j-1]+1);
			}
		}
	}
	printf("%d",f[n][n]);
	return 0;
} 

#include<cctype>
#include<iostream>
#include<cstring>
using namespace std;
int main(){
	string z;
	cin>>z;
	string s="";
	for(int i=0;i<z.length();){
		char ch=z[i];
		if(i+1<z.length()&&isdigit(z[i+1])){
			i++;
			int count=0;
			while(i<z.length()&&isdigit(z[i])){
				count=count*10+(z[i]-'0');
				i++;
			}
			for(int j=0;j<count;++j){
				s+=ch;
			}
		}
		else{
			s+=ch;
			i++;
		}
	}
	cout<<s<<endl;
	return 0;
}

#include<iostream>
#include<vector>
using namespace std;
int N;
bool query(int i,int j);
int main(){
	cin>>N;
	int candidate=0;
	int count=1;
	for(int i=1;i<N;++i){
		if(count==0){
			candidate=i;
			count=1;
		}
		else{
			if(query(candidate,i)==false||query(i,candidate)==false){
				count--;
			}
			else{
				count++;
			}
		}
	}
	cout<<candidate<<endl;
	return 0;
}