// 1539. Kth Missing Positive Number #include /* * given array 'arr' of positive integers sorted in a strictly increasing order, * and an integer 'k', return 'kth' positive integer missing from array -- o(log * n) */ int findKthPositive(int *arr, int arr_size, int k) { int l = 0, r = arr_size, m; while (l < r) { m = (l + r) / 2; if (arr[m] - 1 - m < k) l = m + 1; else r = m; } return l + k; } int main() { int a1[] = {2, 3, 4, 7, 11}, a2[] = {1, 2, 3, 4}; printf("%d\n", findKthPositive(a1, 5, 5)); // expect: 9 printf("%d\n", findKthPositive(a2, 2, 4)); // expect: 6 }