Python 刷Leetcode题库，顺带学英语单词（13）

Rotate Image

You are given an n x n 2D matrix representing an image.
Rotate the image by 90 degrees (clockwise).     [#48]
Note:
You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.

Example 1:
Given input matrix =
[
[1,2,3],
[4,5,6],
[7,8,9]
],
rotate the input matrix in-place such that it becomes:
[
[7,4,1],
[8,5,2],
[9,6,3]
]

Example 2:
Given input matrix =
[
[ 5, 1, 9,11],
[ 2, 4, 8,10],
[13, 3, 6, 7],
[15,14,12,16]
],
rotate the input matrix in-place such that it becomes:
[
[15,13, 2, 5],
[14, 3, 4, 1],
[12, 6, 8, 9],
[16, 7,10,11]
]

Group Anagrams

Given an array of strings, group anagrams together.    [#49]

Example:
Input: ["eat", "tea", "tan", "ate", "nat", "bat"],
Output:
[
["ate","eat","tea"],
["nat","tan"],
["bat"]
]

Note:
All inputs will be in lowercase.
The order of your output does not matter.

Pow(x, n)

Implement pow(x, n), which calculates x raised to the power n (xn).    [#50]

Examples:
Input: 2.00000, 10
Output: 1024.00000
Input: 2.10000, 3
Output: 9.26100
Input: 2.00000, -2
Output: 0.25000
Explanation: 2^-2 = (1/2)^2 = 1/4 = 0.25

Note:
-100.0 < x < 100.0
n is a 32-bit signed integer, within the range [−2^31, 2^31− 1]