算法竞赛入门经典课后习题2

习题2-1

#include<iostream>
#include<math.h>
using namespace std;
int main(){
int x,n;

	while(cin>>x){
		n=0;
	while(x){
		x/=10;
		n++;
	}
	cout<<n<<endl;
	}
	return 0;
}

习题2-2

#include<iostream>
#include<math.h>
using namespace std;
int main(){
int x,a,b,c;
for(x=100;x<1000;x++){
	a=x/100;
	b=(x/10)%10;
	c=x%10;
	if(x==a*a*a+b*b*b+c*c*c) cout<<x<<endl;
}
return 0;
}

习题2-3

#include<iostream>
#include<math.h>
using namespace std;
int main(){
	int x,y,z,sum;
	while(cin>>x>>y>>z){
		for(sum=10;sum<=100;sum++){
			if(sum%3==x&&sum%5==y&&sum%7==z){	cout<<sum<<endl;
			break;
			}
		
		}
		if(sum==101) cout<<"No answer"<<endl;
		
	}
	return 0;
}

习题2-4

#include<iostream>
#include<math.h>
using namespace std;
int main(){
	int n;
	while(cin>>n){
		for(int i=n;i>0;i--){
			for(int j=0;j<n-i;j++){
				cout<<" ";
			}
			for(int j=0;j<2*i-1;j++){
				cout<<"#";
			}
			cout<<endl;
		}
	}
	return 0;
}

习题2-5

#include<iostream>
#include<math.h>
using namespace std;
int main(){
	int n,i,m;
	freopen("input.txt","r",stdin);
	freopen("output.txt","w",stdout);
	while(cin>>n){
	int a[n],N=0;
for(i=0;i<n;i++){
	cin>>a[i];
}
cin>>m;
for(int j=0;j<n;j++){
	if(a[i]<m) N++;
}
cout<<N<<endl;
	}
	return 0;
}

习题2-6

#include<iostream>
#include<math.h>
using namespace std;
int main(){
	int n;
	while(cin>>n){
		float sum=0;
		for(int i=1;i<=n;i++){
			sum+=(float)1.0/i;
		}
		cout.precision(3);
		cout<<fixed<<sum<<endl;
	}
	return 0;
}

习题2-7

#include<iostream>
#include<math.h>
using namespace std;
int main(){
	double n=1,sum=0;
for(int i=1;fabs(n)>1e-6;i++){
	n=pow(-1,i-1)*1.0/(2*i-1);
	sum+=n;
	
}
cout.precision(7);
cout<<sum<<endl;
	return 0;
}

习题2-8

#include<iostream>
#include<math.h>
using namespace std;
int main(){
	int m,n;
	double x=0;
	while(cin>>n>>m){

		for(int i=n;i<=m;i++){
			if(n>sqrt(pow(10,5))) {
				x=0.00001;break;
			}
			if(i*i>pow(10,5)) break;
			x+=1.0/(i*i);
		}
		cout.precision(5);
		cout<<fixed<<x<<endl;
		
	}
	return 0;
}

习题2-9

#include<iostream>
#include<math.h>
using namespace std;
int main(){
	int a,b,c;
	double x=0;
	while(cin>>a>>b>>c){
	x=(double)a/b;
		cout.precision(c);
		cout<<fixed<<x<<endl;
		
	}
	return 0;
}

习题2-10

#include<iostream>
#include<set>
using namespace std;
int ins(set<int> &s,int x){
	for(int i=0;i<3;i++){
		s.insert(x%10);
		x/=10;
	}
	return 1;
	
}
int main(){
	int x,y,z;
	set<int> s;
for(x=123;x<333;x++){
	s.clear();
	y=2*x;
	z=3*x;
	ins(s,x);
	ins(s,y);
	ins(s,z);
if(s.size()==9)
cout<<x<<" "<<y<<" "<<z<<endl;	
}
	return 0;
}