friend（杭电1719）

Friend

Time Limit: 1000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 1994    Accepted Submission(s): 1003

Problem Description

Friend number are defined recursively as follows.
(1) numbers 1 and 2 are friend number;
(2) if a and b are friend numbers, so is ab+a+b;
(3) only the numbers defined in (1) and (2) are friend number.
Now your task is to judge whether an integer is a friend number.

 

Input

There are several lines in input, each line has a nunnegative integer a, 0<=a<=2^30.

 

Output

For the number a on each line of the input, if a is a friend number, output “YES!”, otherwise output “NO!”.

 

Sample Input

31312112131

 

Sample Output

YES!YES!NO!

 

Source

2007省赛集训队练习赛（2）

 

解题思路：参考题解

#include<stdio.h>int main(){int n;while(scanf("%d",&n)!=EOF){if(n==0){printf("NO!\n");continue;}n++;while(n){if(n%2==0)   n/=2;else   break;}while(n){if(n%3==0)   n/=3;else   break;}if(n==1)printf("YES!\n");elseprintf("NO!\n");}return 0;}