[Solved] A permutation perm of n + 1 integers of all the integers in the range [0, n] can be represented as a string s of length n where: s[i] == ‘I’ if perm[i] < perm[i + 1], and s[i] == 'D' if perm[i] > perm[i + 1].
[Solved] Given the root node of a binary search tree and two integers low and high, return the sum of values of all nodes with a value in the inclusive range [low, high].
[Solved] Every valid email consists of a local name and a domain name, separated by the ‘@’ sign. Besides lowercase letters, the email may contain one or more ‘.’ or ‘+’. For example, in “alice@leetcode.com”, “alice” is the local name, and “leetcode.com” is the domain name.
[Solved] Your friend is typing his name into a keyboard. Sometimes, when typing a character c, the key might get long pressed, and the character will be typed 1 or more times.
[Solved] Given an integer array nums, move all the even integers at the beginning of the array followed by all the odd integers. Return any array that satisfies this condition.
[Solved] Given the root of a binary search tree, rearrange the tree in in-order so that the leftmost node in the tree is now the root of the tree, and every node has no left child and only one right child.
[Solved] A sentence is a string of single-space separated words where each word consists only of lowercase letters.
[Solved] Given the head of a singly linked list, return the middle node of the linked list. If there are two middle nodes, return the second middle node.
[Solved] Consider all the leaves of a binary tree, from left to right order, the values of those leaves form a leaf value sequence.