Lucky Numbers (easy)

 

一道超级简单的BFS

 

 

#include<bits/stdc++.h>
using namespace std;
bool islucky(long long x){
    int cnt4=0,cnt7=0;
    while(x){
        int temp=x%10;
        if(temp==4){
            cnt4++;
        }
        if(temp==7){
            cnt7++;
        }
        x/=10;
    }
    if(cnt4==cnt7){
        return true;
    }
    return false;
}
int main()
{
    queue<long long> q;
    long long n;
    cin>>n;
    long long ans=0;
    q.push(ans);//记得放入队列
    while(true){
        ans=q.front();
        q.pop();
        if(ans>=n&&islucky(ans)){
            cout<<ans;
            break;
        }
        q.push(ans*10+4);
        q.push(ans*10+7);
    }
    return 0;
}