86 lines
2.6 KiB
Markdown
86 lines
2.6 KiB
Markdown
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- 中国地下乐队
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collapsed:: true
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- 退格 backspace (psychedelic rock
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- 兵马司（发行）
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- Re tros (daft funk
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- Dream can
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- Leetcode - Rotate Image
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id:: 64422d1f-5db3-435d-ab4e-2b9fe5fd47cd
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collapsed:: true
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- Times:
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- Time when completed: 14:28
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- Time taken to complete: 15 mins ( with solution in mind )
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- DONE Revisions:
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SCHEDULED: <2023-05-26 Fri>
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:LOGBOOK:
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* State "DONE" from "LATER" [2023-04-28 Fri 16:45]
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* State "DONE" from "LATER" [2023-05-23 Tue 20:26]
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:END:
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-
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- Tags:
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- Algorithms: #math
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- Data structures: #array
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- Difficulty: #difficulty_easy
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- Platforms: #leetcode
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- Links:
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- [link to the problem](https://leetcode.com/problems/rotate-image/description/)
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- Problem:
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- You are given an `n x n` 2D `matrix` representing an image, rotate the image by **90** degrees (clockwise).
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- You have to rotate the image [**in-place**](https://en.wikipedia.org/wiki/In-place_algorithm), which means you have to modify the input 2D matrix directly. **DO NOT** allocate another 2D matrix and do the rotation.
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- Examples:
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- https://assets.leetcode.com/uploads/2020/08/28/mat1.jpg
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- https://assets.leetcode.com/uploads/2020/08/28/mat2.jpg
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- ```
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Example 1:
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Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]
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Output: [[7,4,1],[8,5,2],[9,6,3]]
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Example 2:
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Input: matrix = [[5,1,9,11],[2,4,8,10],[13,3,6,7],[15,14,12,16]]
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Output: [[15,13,2,5],[14,3,4,1],[12,6,8,9],[16,7,10,11]]
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```
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- Constraints:
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- `n == matrix.length == matrix[i].length`
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- `1 <= n <= 20`
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- `-1000 <= matrix[i][j] <= 1000`
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- Thoughts:
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- Intuition:
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- The solution is tricky, which requires you to use math.
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- In order to do this, first, transpose, then reflect the matrix.
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- Solution:
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- java
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- ```java
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class Solution {
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private void swap(int[][] matrix, int a, int b, int x, int y) {
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int temp = matrix[a][b];
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matrix[a][b] = matrix[x][y];
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matrix[x][y] = temp;
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}
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public void rotate(int[][] matrix) {
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// transpose and reflect
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for (int i = 0; i < matrix.length; i++) {
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for (int j = 0; j < i; j++) {
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swap(matrix, i, j, j, i);
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}
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}
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for (int i = 0; i < matrix.length; i++) {
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for (int j = 0; j < matrix.length / 2; j++) {
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swap(matrix, i, j, i, matrix.length - j - 1);
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}
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}
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}
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}
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```
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- DONE 购物清单 [[Shopping lists]]
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- DONE 香熏/香氛
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- DONE 耳塞
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- DONE 查英语成绩
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SCHEDULED: <2023-04-25 Tue>
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- DONE 报名
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SCHEDULED: <2023-05-08 Mon>
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- DONE 写乐理练习的作业
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