Given a collection of distinct numbers, return all possible permutations.

Example:

[1,2,3] have the following permutations:

1
2
3
4
5
6
7
8

[
  [1,2,3],
  [1,3,2],
  [2,1,3],
  [2,3,1],
  [3,1,2],
  [3,2,1]
]

Reverse a linked list from position m to n. Do it in-place and in one-pass.

For example:

Given 1->2->3->4->5->NULL, m = 2 and n = 4,

return 1->4->3->2->5->NULL.

Note:

Given m, n satisfy the following condition:

1 ≤ m ≤ n ≤ length of list.

Given an index k, return the kth row of the Pascal’s triangle.

Example

given k = 3, Return [1,3,3,1].

Note:

Could you optimize your algorithm to use only O(k) extra space?

Given an array of integers, find out whether there are two distinct indices i and j in the array such that the difference between nums[i] and nums[j] is at most t and the difference between i and j is at most k.

Given an integer array with all positive numbers and no duplicates, find the number of possible combinations that add up to a positive integer target.

Example:

nums = [1, 2, 3] target = 4

The possible combination ways are:

1
2
3
4
5
6
7

(1, 1, 1, 1)
(1, 1, 2)
(1, 2, 1)
(1, 3)
(2, 1, 1)
(2, 2)
(3, 1)

Note:

Different sequences are counted as different combinations.

Therefore the output is 7.

Follow up:

• What if negative numbers are allowed in the given array?
• How does it change the problem?
• What limitation we need to add to the question to allow negative numbers?

Given a string s and a dictionary of words dict, determine if s can be segmented into a space-separated sequence of one or more dictionary words.

For example, given

s = “leetcode”, dict = [“leet”, “code”].

Return true because “leetcode” can be segmented as “leet code”.

Given a binary tree, return the zigzag level order traversal of its nodes’ values. (ie, from left to right, then right to left for the next level and alternate between).

Example:

Given binary tree [3,9,20,null,null,15,7],

1
2
3
4
5

3
   / \
  9  20
/  \
   15   7

return its zigzag level order traversal as:

1
2
3
4
5

[
  [3],
  [20,9],
  [15,7]
]

Implement a trie with insert, search, and startsWith methods.

Note:

You may assume that all inputs are consist of lowercase letters a-z.

Given a binary tree, return the level order traversal of its nodes’ values. (ie, from left to right, level by level).

Example:

Given binary tree [3,9,20,null,null,15,7],

1
2
3
4
5

3
   / \
  9  20
/  \
   15   7

return its level order traversal as:

1
2
3
4
5

[
  [3],
  [9,20],
  [15,7]
]

Given an integer, write a function to determine if it is a powero two.