codeforces-320A-Magic Numbers

http://codeforces.com/problemset/problem/320/A

A magic number is a number formed by concatenation of numbers 1, 14 and 144. We can use each of these numbers any number of times. Therefore 14144, 141414 and 1411 are magic numbers but 1444, 514 and 414 are not.

You're given a number. Determine if it is a magic number or not.

Input

The first line of input contains an integer n, (1 ≤ n ≤ 109). This number doesn't contain leading zeros.

Output

Print "YES" if n is a magic number or print "NO" if it's not.

Sample test(s)
Input
114114
Output
YES
Input
1111
Output
YES
Input
441231
Output
NO

思路：
1、 除了1和4不允许出现其他数字。
2、 4的前2位数只可能是14、41或者11
 1 #include<iostream>
 2 #include<cstdio>
 3 using namespace std;
 4 int main()
 5 {
 6     int n,flag=1;
 7     scanf("%d",&n);
 8     while(n)
 9     {
10         if(n%10==4)
11         {
12             n/=10;
13             if(n%10==4)
14             {
15                 n/=10;
16                 if(n%10!=1)
17                     flag=0;
18             }
19             else if(n%10==1)
20                 n/=10;
21             else
22                 flag=0;
23         }
24         else if(n%10==1)
25             n/=10;
26         else
27             flag=0;
28         if(flag==0)
29         {
30             printf("NO\n");
31             break;
32         }
33     }
34     if(n==0 && flag==1)
35         printf("YES\n");
36     return 0;
37 }
View Code

 

posted @ 2013-06-27 23:37  JKXQJ  阅读(1138)  评论(0)  编辑  收藏  举报