二分探索(ABC 063 D問題)

バグらせまくった
問題
以下ネタバレ注意

1. int N, A, B;
2. int h[100010], x[100010];
3.  
4. //a÷b以上の最小の整数
5. ll CEIL(ll a, ll b) {
6. return (a + b - 1) / b;
7. }
8.  
9. bool isOK(ll K) {
10. ll cnt = 0;
11. REP(i, N) {
12. if (B*K < h[i]) {
13. cnt += CEIL(h[i] - B * K, A - B);
14. }
15. }
16. if (cnt <= K)return true;
17. else return false;
18. }
19.  
20. int binary_search() {
21. int ng = -1;
22. ll ok = 1000000001;
23.  
24. while (abs(ok - ng) > 1) {
25. ll mid = (ok + ng) / 2;
26.  
27. if (isOK(mid)) ok = mid;
28. else ng = mid;
29. }
30. return ok;
31. }
32.  
33. int main() {
34. cin >> N >> A >> B;
35. REP(i, N) {
36. cin >> h[i];
37. }
38.  
39. ll ans = binary_search();
40. cout << ans << endl;
41. }