[ARC075B] Widespread

[ARC075B] Widespread

题意：给(n)个人血量，然后一次攻击只能对一个人造成(a)伤害，对其他人造成(b)伤害，求最少次数打败全部敌人。
题解：二分我是没想到的，直接二分次数，然后(O(n))判断是否能全打败就可以了。
代码：

#include <algorithm>
#include <cmath>
#include <cstdio>
#include <iostream>
#include <map>
#include <vector>

using namespace std;
typedef long long ll;
const ll N = 1e5 + 99;
const ll Max = 1e9 + 99;
ll h[N];
ll first[N];
ll a, b;
ll n;
bool check(ll mid) {
    ll cnta = mid;
    for (int i = 1; i <= n; i++) {
        if (h[i] - mid * b <= 0) {
            continue;
        } else {
            ll d = h[i] - mid * b;
            ll dd = a - b;
            ll Cnt = d / dd + (d % dd == 0 ? 0 : 1);
            cnta -= Cnt;
        }
    }
    if (cnta < 0) {
        return 1;
    } return 0;
}
void solve() {

   cin >> n;
    cin >> a >> b;
    for (ll i = 1; i <= n; i++) {
        cin >> h[i];
    }
    ll cnt = 0;
    sort(h + 1, h + 1 + n);
    ll l = 0, r = Max;
    while ( l < r) {
        ll mid = (l + r) >> 1;
        if (check(mid)) {
            l = mid + 1;
            //cout << "?0;";
        } else {
            r = mid;
            //cout << "))_
";
        }
        //cout << l << " " << r << endl;
    }
    cout << l << endl;
}
signed main() {
    ll t = 1;
    //cin >> t;
    while (t--) {
        solve();
    }
}