Given a digit string, return all possible letter combinations that the number could represent.

A mapping of digit to letters (just like on the telephone buttons) is given below.

Example

Input:Digit string “23”

Output: [“ad”, “ae”, “af”, “bd”, “be”, “bf”, “cd”, “ce”, “cf”].

Note

Although the above answer is in lexicographical order, your answer could be in any order you want.

You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Follow up: Could you do this in-place?

Write a function that takes a string as input and returns the string reversed.

Example

Given s = “hello”, return “olleh”.

Follow up for “Remove Duplicates”: What if duplicates are allowed at most twice?

Example

Given sorted array nums = [1,1,1,2,2,3],

Your function should return length = 5, with the first five elements of nums being 1, 1, 2, 2 and 3. It doesn’t matter what you leave beyond the new length.

Given a linked list, return the node where the cycle begins. If there is no cycle, return null.

Note

Do not modify the linked list.

Follow up

Can you solve it without using extra space?

Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

Example

Given the following binary tree,

1
2
3
4
5
6

   1            <---
 /   \
2     3         <---
 \     \
  5     4       <---
You should return [1, 3, 4].

Given two binary strings, return their sum (also a binary string).

Example,

1
2
3

a = "11"
b = "1"
Return "100".

Implement pow(x, n).

Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers.

If such arrangement is not possible, it must rearrange it as the lowest possible order (ie, sorted in ascending order).

The replacement must be in-place, do not allocate extra memory.

Here are some examples. Inputs are in the left-hand column and its corresponding outputs are in the right-hand column.

1
2
3

1,2,3 → 1,3,2
3,2,1 → 1,2,3
1,1,5 → 1,5,1

A robot is located at the top-left corner of a m x n grid (marked ‘Start’ in the diagram below).

The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid (marked ‘Finish’ in the diagram below).

How many possible unique paths are there?

Note

m and n will be at most 100.