Codeforces Round #644 (Div. 3) H——Binary Median 二分

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int maxn=1e6+7;
#define int long long
int a[107];
int n,m;
int check(int x)
{
    int ret=x;
    for (int i=1; i<=n; i++)
        if (a[i]<=x) 
            ret--;
    ret++;
    return ret>=((1ll<<m)-n-1)/2+1;
}
signed main()
{
    int t;
    cin>>t;
    while (t--)
    {
        cin>>n>>m;
        for (int i=1; i<=n; i++)
        {
            string s;
            cin>>s;
            int now=0;
            for (char c:s) 
                now=now*2+(c-'0');
            a[i]=now;
        }
        int l=0,r=(1ll<<m);
        while(l<r)
        {
            int mid=(l+r)>>1;
            if (check(mid)) 
                r=mid;
            else 
                l=mid+1;
        }
        vector<int> v;
        for (int i=0; i<m; i++)
            v.push_back(r&1),r>>=1;
        reverse(v.begin(),v.end());
        for (int i:v) cout<<i;
        cout<<endl;
    }
}