n*n matrix, find the
kth smallest element. Each row in the matrix is sorted in ascending order and independent of the other rows. Do not use
O(n*n) space when solving this. One example matrix looks like this:
If we could use all the space we wanted, we could just perform an n-way merge sort on every row at once. This would work because the rows itself are sorted already. Afterwards, we would need to pick the kth element from the list and would be done.
head of a list with pointers to
next and a
random element, copy the list to a new list without any random pointers pointing to the old list.
Characters can be encoded via different numbers.
A -> 1, B -> 2, ..., Z -> 26. Given a string
s of numbers, return the number of possible decodings. For example
12 can be decoded as
A,B and as
Given two lists of a
inorder, create a tree and return the
The problem is not so obvious at first. If the preorder list would also contain
null values for the places where the tree does not contain nodes, we could simply iterate over this list and reconstruct the tree from there. But since the
null values are missing, we also need to take a look at the
root node of a tree, validate whether it is a valid Binary Search Tree. This is a tree where each node is unique, left children are smaller than the root and right children are greater than the root.