cf 189 div2 A - Magic Numbers

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本文介绍了一种判断特定形式的魔法数字的方法。这些数字由1、14和144构成，可以任意组合出现。通过示例解释了如何使用该方法，并提供了一个简单的C++代码实现。

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水题。下面是代码：#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#define inf 1000000000
using namespace std;

int main(){
    //freopen("input.txt","r",stdin);
    //freopen("output.txt","w",stdout);
    char s[100];
    cin>>s;
    int i,j;
    int l=strlen(s);
    for(i=0;i<l;i++){
         if(s[i]!='1'&&s[i]!='4')
            break;
    }
    if(i<l||s[0]!='1'){
         cout<<"NO"<<endl;
         return 0;
    }
    for(i=0;i<l;i++){
         if(s[i]!='1') continue;
         for(j=i+1;j<l;j++){
             if(s[j]=='1') break;
         }
          if(j-i>3){
             cout<<"NO"<<endl;
             return 0;
          }
    }
    cout<<"YES"<<endl;
    return 0;
}