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Question

A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.

Return a deep copy of the list.

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Question

Given a reference of a node in a connected undirected graph.

Return a deep copy (clone) of the graph.

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Question

A binary tree is given such that each node contains an additional random pointer which could point to any node in the tree or null.

Return a deep copy of the tree.

The tree is represented in the same input/output way as normal binary trees where each node is represented as a pair of [val, random_index] where:

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Question

Given an unsorted array of integers, find the length of the longest consecutive elements sequence.

Your algorithm should run in O(n) complexity.

Example:
Input: [100, 4, 200, 1, 3, 2]
Output: 4
Explanation: The longest consecutive elements sequence is [1, 2, 3, 4]. Therefore its length is 4.

Question

You have a queue of integers, you need to retrieve the first unique integer in the queue.

Implement the FirstUnique class:

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Question

1480. Running Sum of 1d Array

      Given an array nums. We define a running sum of an array as runningSum[i] = sum(nums[0]…nums[i]).

      Return the running sum of nums.

      Example 1:
      Input: nums = [1,2,3,4]
      Output: [1,3,6,10]
      Explanation: Running sum is obtained as follows: [1, 1+2, 1+2+3, 1+2+3+4].

Question

You have 4 cards each containing a number from 1 to 9. You need to judge whether they could operated through *, /, +, -, (, ) to get the value of 24.

Example 1:
Input: [4, 1, 8, 7]
Output: True
Explanation: (8-4) * (7-1) = 24

Question

1470. Shuffle the Array

      Given the array nums consisting of 2n elements in the form [x1,x2,…,xn,y1,y2,…,yn].

      Return the array in the form [x1,y1,x2,y2,…,xn,yn].

      Example 1:
      Input: nums = [2,5,1,3,4,7], n = 3
      Output: [2,3,5,4,1,7]
      Explanation: Since x1=2, x2=5, x3=1, y1=3, y2=4, y3=7 then the answer is [2,3,5,4,1,7].

Question

Two elements of a binary search tree (BST) are swapped by mistake.
Recover the tree without changing its structure.

Example 1:
Input: [1,3,null,null,2]

1 2 3 4 5

1 / 3 \ 2

Output: [3,1,null,null,2]

1 2 3 4 5

3 / 1 \ 2

Question

Given n, how many structurally unique BST’s (binary search trees) that store values 1 … n?

Example:
Input: 3
Output: 5

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