Findable Numbers

Donald duck loves learning new algorithms. Today, he learned binary search and understood how it works on integer arrays sorted in non-decreasing order. His knack of getting into problems is famous, and he wrote his version of binary search algorithm as follows: binarySearch(int[] array, int lo, int hi, int key) { while (lo ≤ hi) { mid := random(lo, hi); if a[mid] = key then return mid;