Given preorder and inorder traversal of a tree, construct the binary tree.

Given a balanced parentheses string S, compute the score of the string based on the following rule:

Sort a linked list in O(n log n) time using constant space complexity.

Given a non-empty 2D array grid of 0’s and 1’s, an island is a group of 1’s (representing land) connected 4-directionally (horizontal or vertical.) You may assume all four edges of the grid are sur…

Given a string, your task is to count how many palindromic substrings in this string.

Each value v = grid[i][j] represents a tower of v cubes placed on top of grid cell (i, j).

Given a string S, return the “reversed” string where all characters that are not a letter stay in the same place, and all letters reverse their positions.

A sentence S is given, composed of words separated by spaces. Each word consists of lowercase and uppercase letters only.

Given a sorted array consisting of only integers where every element appears twice except for one element which appears once. Find this single element that appears only once.

Given a linked list, remove the n-th node from the end of list and return its head.给定一个链表，删除链表的倒数第 n 个节点，并且返回链表的头结点。