算法15---数论2---亲密数

算法16---数论2---亲密数

如果整数a的因子和等于整数b，整数b的因子和等于整数a，因子包括1但不包括本身，且a不等于b，则称a和b为亲密数对。

/*
    题目：亲密数
    author taoliu——alex  2016.10

    主要实现两种
    1 判断两个数是不是亲密数。
    2 找出一定范围内的亲密数。

*/


#include <stdio.h>
#include <stdlib.h>

int  friendnum(int a,int b);
int factor_sum(int n);
void scope_friendnum(int scope);

//判断两个数是不是亲密数。

int  friendnum(int a,int b)
{
    if (a==b)
    {
        return -1;
    }
    int a_sum=0;
    int b_sum=0;
    a_sum=factor_sum(a);
    b_sum=factor_sum(b);
    //printf("the factor sum of %d is %d
",a,a_sum);
    //printf("the factor sum of %d is %d
",b,b_sum);
    if ((a_sum==b)&&(b_sum==a))
    {
        return 1;
    }
    else
    {
        return 0;
    }

}

int factor_sum(int n)
{
    int sum=0;
    for (int i = 1; i < n/2+1; i++)
    {
        if (n%i==0)
        {
            sum=sum+i;
        }
    }
    return sum;
}

// 找出一定范围内的亲密数。
void scope_friendnum(int scope)
{
    for (int i = 1; i < scope; i++)
    {
        for (int j = i; j < scope; j++)
        {
            int ans=friendnum(i,j);
            if(ans==1)
                printf("%d and %d is friendnum
",i,j);
        }
    }
}


int main()
{
    int judge;
    int a,b,scope;
    printf("what you want to do :  0 means judge two number is friendnum or not;
");
    printf(" 1 means you want to find the friendnum in scope
");
    //fflush(stdin);
    scanf("%d",&judge);
    if (judge==0)
    {
        printf("input two number you want to judge!
");
        //fflush(stdin);
        scanf("%d%d",&a,&b);
        int ans=friendnum(a, b);
        if (ans==1)
        {
            printf("%d and %d is friendnum
",a,b);
        }
        if (ans==0)
        {
            printf("%d and %d is not friendnum
",a,b);
        }
        else
            printf("%d and %d is the same number ,error!
", a,b);
    }
    if (judge==1)
    {
        printf("input the scope you want to find
");
        //fflush(stdin);
        scanf("%d",&scope);
        scope_friendnum(scope);
    }
    return 0;
}