_a_plane_journey_binary_search.cpp

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
bool check (int a[], int b[], int mid, int i, int j){
	while (i >= 0 and j >= 0){
        if (a [i] > b [j]) return 0;
        i -= mid;
        j -= 1;}
    if (j < 0 and i >= 0) return 0;
    return 1;
}
int main(){
    ios::sync_with_stdio(0), cin.tie(0);
	int n, m;
	cin >> n >> m;
	int m1 = m - 1, n1 = n - 1;
    int a [n], b [m];
	for (int i = 0; i < n; i++)
        cin >> a[i];
    for (int i = 0; i < m; i++)
        cin >> b[i];
    sort (a, a + n);
    sort (b, b + m);
    if (b [m1] < a [n1])
        return cout << "-1\n", 0;
    int lo = 0, hi = n;
    while (lo < hi){
        int mid = (lo + hi) / 2;
		if (check (a, b, mid, n1, m1)) hi = mid;
		else lo = mid + 1;
    }
    cout << hi * 2 - 1 << '\n';
}