table of Contents
Question A: [Introduction to Recursion] All permutations [Simple]
http://codeup.cn/problem.php?cid=100000608&pid=0
#include<cstdio>
#include<string>
#include<cstring>
#include<iostream>
#include<algorithm>
#define max 15
using namespace std;
int a[max];//保存记录
int n;
bool b[max];//保存当前的状态
void dfs(int index)
{
if(index==n+1)
{
for(int i=1;i<=n;i++)
{
printf("%d ",a[i]);
}
printf("\n");
return;
}
int i;
for(i=1;i<=n;i++)
{
if(b[i]==false)
{
b[i]=true;
a[index]=i;
dfs(index+1);
b[i]=false;//恢复现场
}
}
}
int main(void)
{
cin>>n;
dfs(1);
return 0;
}
Question B: [Introduction to Recursion] The output of the combination [Simple]
http://codeup.cn/problem.php?cid=100000608&pid=1
#include<cstdio>
#include<string>
#include<cstring>
#include<iostream>
#include<algorithm>
#define max 15
using namespace std;
int a[max];
int n;
int r;
bool b[max];
void dfs(int index,int start)//当前选的是第几个数, strat从哪里开始选 确保不重复
{
if(index==r+1)
{
for(int i=1;i<=r;i++)
{
printf("%d ",a[i]);
}
printf("\n");
return;
}
int i;
for(i=start;i<=n;i++)
{
if(b[i]==false)
{
b[i]=true;
a[index]=i;
dfs(index+1,i);
b[i]=false;
}
}
}
int main(void)
{
cin>>n>>r;
dfs(1,1);
return 0;
}
Question C: [Introduction to Recursion] Combination + Judging Prime Numbers [中]
http://codeup.cn/submitpage.php?cid=100000608&pid=2&langmask=0
#include<cstdio>
#include<string>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<cmath>
#include<map>
#define max 30
using namespace std;
int a[max];//数据
int c[max];//保存选的方式
bool b[max];//选没选
int n;
int k;
int ans=0;//总数
//map<int,bool>ways;//记录这个数选没选
bool judge(int sum)
{
int i=2;
if(sum==2)
return true;
if(sum==1)
return false;
while(i<= (int)sqrt(1.0*sum) )
{
if(sum%i==0)
return false;
i++;
}
return true;
}
void dfs(int index,int start)
{
if(index==k+1)
{
long long sum=0;
for(int i=1;i<=k;i++)
{
sum+=c[i];
}
if(judge(sum))
{
ans++;
}
return;
}
int i;
for(i=start;i<=n;i++)
{
if(b[i]==false)
{
b[i]=true;
c[index]=a[i];
dfs(index+1,i);
b[i]=false;
}
}
}
int main(void)
{
while(cin>>n>>k)
{
for(int i=1;i<=n;i++)
{
cin>>a[i];
}
dfs(1,1);
printf("%d\n",ans);
ans=0;
}
return 0;
}