算法思想：
循环求出每个数中1的个数，累计之，若满足f(n)=n，则退出，否则继续。
代码如下：
/**//**************************
* 0~n之间1的个数,如f(13)=6
* 1,2,3,4,5,6,7,8,9,10,11,12,13.1的个数为6
* 要求:输入一个正整数n,求出f(n),及求解f(n)=n
***********************/
#include <stdio.h>
#include <string.h>
#include <Windows.h>
class CalculationTimes
...{
public:
CalculationTimes()...{}
~CalculationTimes()...{}
int GetTimes(int n);
};
//计算正整数n中1的个数
int CalculationTimes::GetTimes(int n)
...{
int count=0;
while(n)
...{
if(n%10==1)
count++;
n/=10;
}
return count;
}
//显示菜单
void show_menu()
...{
printf(\"--------------------------------------------- \");
printf(\"input command to test the program \");
printf(\" i or I : input n to test \");
printf(\" g or G : get n to enable f(n)=n \");
printf(\" q or Q : quit \");
printf(\"--------------------------------------------- \");
printf(\"$ input command >\");
}
void main()
...{
char sinput[10];
int n;
show_menu();
scanf(\"%s\",sinput);
while(stricmp(sinput,\"q\")!=0)
...{
int t=0,count=0;
if(stricmp(sinput,\"i\")==0)
...{
printf(\" please input an integer:\");
scanf(\"%d\",&n);
count=0;
CalculationTimes obj;
t=GetTickCount();
for(int i=1;i<=n;i++)
count+=obj.GetTimes(i);
t=GetTickCount()-t;
printf(\" count=%d time=%d \",count,t);
}
else if(stricmp(sinput,\"g\")==0)
...{
CalculationTimes obj;
n=2;
count=1;
t=GetTickCount();
while(1)
...{
count+=obj.GetTimes(n);
if(count==n)
break;
n++;
}
t=GetTickCount()-t;
printf(\" f(n)=n=%d time=%d \",n,t);
}
//输入命令
printf(\"$ input command >\");
scanf(\"%s\",sinput);
}
}
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