codeforces 915 C(思维+模拟)

#include <iostream>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <string>
#include <map>
#include <iomanip>
#include <algorithm>
#include <queue>
#include <stack>
#include <set>
#include <vector>
//const int maxn = 1e5+5;
#define ll long long
#define inf 0x3f
#define FOR(i,a,b) for( int i = a;i <= b;++i)
#define bug cout<<"--------------"<<endl
#define bugs cout<<"SSSSSSSSSSSSSSS"<<endl

ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
ll lcm(ll a,ll b){return a/gcd(a,b)*b;}
const int maxn = 5100;
using namespace std;
int a[50],b[50],vis[50],cun[50];
int t[50];
int tail1,tail2;

int n;
int findsame(int k)
{
    for(int i = 1;i <= n; ++i)
    {
        if(a[i] == b[k] && vis[i] == 0) return i;
    }
    return 0;
}
int findsmall(int k)
{
    for(int i = 1;i <= n; ++i)
    {
        if(a[i] < b[k] && vis[i] == 0) return i;
    }
    return 0;
}
int main()
{
    
    //freopen("C:\\ACM\\input.txt","r",stdin);
    ll x,y;
    cin>>x>>y;
     tail1 = 0;
     tail2 = 0;
    while(x)
    {
        a[++tail1] = x % 10;
        x /= 10;
    }
    while(y)
    {
        b[++tail2] = y % 10;
        y /= 10;
    }    
    sort(a+1,a+tail1+1);
    reverse(a+1,a+1+tail1);
    reverse(b+1,b+1+tail2);

    if(tail1 < tail2 )
    {
        for(int i = 1;i <= tail1; ++i)
            cout<<a[i];
    }
    else 
    {
        n = tail1;
        int flag = 0;
        int Head = 0;
        stack<int>sta;
        for(int i = 1;i <= n; ++i)
        {

            if(flag == 1)
            {
                int temp = sta.top();sta.pop();
                vis[temp] = 0;
                if(findsmall(i) != 0)
                {
                    
                    cun[i] = a[findsmall(i)];
                    Head = i;
                    vis[findsmall(i)] = 1;
                    break;
                } 
                else i-=2;
                continue;
            }
            if(findsame(i) != 0)
            {
                cun[i] = a[findsame(i)];
                sta.push(findsame(i));
                //cout<<findsame(i)<<endl;
                
                vis[findsame(i)] = 1; 
                
                
            }
            else if(findsmall(i) != 0)
            {
                cun[i] = a[findsmall(i)];
                sta.push(findsmall(i));


                Head = i ;
                vis[findsmall(i)] = 1;
                
                break;
            }
            else 
            {
                i -= 2;
                flag = 1;
            }
            if(i == n) Head = n;
        }


/*        for(int i = 1;i <= n; ++i) cout<<vis[i]<<" ";
        cout<<endl;
        bug;*/
        for(int i = 1;i <= Head; ++i) cout<<cun[i]; 
        for(int i = 1;i <= n; ++i) if(vis[i] ==0) cout<<a[i];

    }
}