A. Magic Numbers 模拟

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.

Examples
inputCopy
114114
outputCopy
YES
inputCopy
1111
outputCopy
YES
inputCopy
441231
outputCopy
NO

统计1 后面4 的个数即可，模拟就行了

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define inf 0x3f3f3f3f
#define maxn 2005
const int mod=1e9+7;
#define eps 1e-5
#define pi acos(-1.0)

ll quickpow(ll a,ll b)
{
    ll ans=1;
    while(b){
        if(b&1){
            ans=ans*a;
        }
        a=a*a;
        b>>=1;
    }
    return ans;
}
ll gcd(ll a,ll b)
{
    return b==0?a:gcd(b,a%b);
}


int main()
{
    ios::sync_with_stdio(false);
    string s;
    cin>>s;
    int len=s.length();
    int i,j;
    int flag=0;
    int cnt;
    for(i=0;i<len;i++){
        if(s[i]!='1'){
            flag=1;
            break;
        }
        if(s[i]=='1'){
                 cnt=0;
            for(j=i+1;j<len;j++){

                if(s[j]=='4'){
                    cnt++;
                if(cnt>2){
                    flag=1;
                   // cout<<cnt<<endl;
                    break;
                }
                }
                else break;
            }
            i=j-1;
        }

    }
   // cout<<cnt<<endl;
    if(flag)cout<<"NO"<<endl;
    else cout<<"YES"<<endl;
}