Problem description:

Given an encoded string, return its decoded string.

Problem description:

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 surrounded by water.

Problem description:

Create a timebased key-value store class TimeMap, that supports two operations.

Problem description:

Given an array of points where points[i] = [xi, yi] represents a point on the X-Y plane and an integer k, return the k closest points to the origin (0, 0).

CAP:

• Consistency: Assuming you have a storage system which has more than one machine, consistency implies that the data is same across the cluster, so you can read or write to/from any node and get the same data.

Problem description:

Design a simplified version of Twitter where users can post tweets, follow/unfollow another user, and is able to see the 10 most recent tweets in the user’s news feed.

List

1. Create list

   1 2 3

   a = [0, 1, 2] a.append(3) # a = [0, 1, 2, 3] a += [4] # a = [0, 1, 2, 3, 4]

Problem description:

Given the root of a binary tree, return the postorder traversal of its nodes’ values.

Problem description:

Solution:

time complexity: $O()$
space complexity: $O()$
reference:
related problem:

Problem description:

Given a collection of numbers, nums, that might contain duplicates, return all possible unique permutations in any order.