清北学堂模拟赛d6t1 角谷猜想

#include <bits/stdc++.h>
#define N 100005
using namespace std;
int n,top;
char c[N],st[N];
int main()
{
    freopen("kakutani.in","r",stdin);
    freopen("kakutani.out","w",stdout);
    cin>>n;
    while(n--)
    {
        scanf("%s",c+1);
        int l=strlen(c+1);
        for(int i=1;i<=l;i++)
        {
            if(c[i]!=‘4‘&&c[i]!=‘7‘)
                if(c[i]==‘3‘&&st[top]==‘1‘)top--;
                    else st[++top]=c[i];
        }
        if(!top)cout<<0;for(int i=1;i<=top;i++)cout<<st[i];cout<<endl;
        top=0;
    }

    return 0;
}