Counting triplets

Array Game

Educational Codeforces Round 40 (Rated for Div. 2) G. Castle Defense

Helvetic Coding Contest 2018 online mirror (teams allowed, unrated) A2. Death Stars (medium)

Helvetic Coding Contest 2018 online mirror (teams allowed, unrated) C2. Encryption (medium)

Educational Codeforces Round 41 (Rated for Div. 2) D. Pair Of Lines

Tinkoff Internship Warmup Round 2018 and Codeforces Round 475 (Div. 1) B. Destruction of a Tree

501. Find Mode in Binary Search Tree

Given the root of a binary search tree (BST) with duplicates, return all the mode(s)) (i.e., the most frequently occurred element) in it.

If the tree has more than one mode, return them in any order.

Assume a BST is defined as follows:

• The left subtree of a node contains only nodes with keys less than or equal to the node’s key.
• The right subtree of a node contains only nodes with keys greater than or equal to the node’s key.
• Both the left and right subtrees must also be binary search trees.

Palindromes Everywhere

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