[21 Days Learning Challenge] Image rotation problem (two-dimensional array)

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活动地址：CSDN21天学习挑战赛

怕什么真理无穷,A further joy.

【21天学习挑战赛】图像的旋转问题(二维数组)

Why am I participating in the Challenge

1,机缘

read the first grade,The summer vacation device opened a private message and found that this challenge had the courage to participate.

2,Expected harvest

A, I am studying for a master's degree at South China University of Technology,The current research direction is image restoration,从事深度学习相关工作,The goal is to engageJava后端开发.
B, 期待您的反馈,如果有什么不对的地方,欢迎指正！
C, Looking forward to meeting like-minded peers or technical exchanges.
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什么是二维数组？

二维数组是一种结构较为特殊的数组,只是将数组中的每个元素变成了一维数组.所以在JavaThe essence of a two-dimensional array in is still a one-dimensional array,内部的一维数组仍然从索引 0 开始,我们可以将它看作一个矩阵,并处理矩阵的相关问题

Definition of the rotation of an image

Refers to the rotation of an image by a certain angle around a certain point,形成一幅新的图像的过程.Of course this point is usually the center of the image.Since it is rotated according to the center,Naturally there is such a property：The position of the point from the center before and after the rotation does not change.

Steps for image rotation

1. 如果是顺时针旋转90°：It must be flipped diagonally first,再水平翻转
2. If it is counterclockwise90°：It must be flipped horizontally first,再对角线翻转

Diagonal flip step
红色为分割线,按照橙色线进行数据绿色pair-wise exchange(matrix[i][j],matrix[j][i] = matrix[j][i],matrix[i][j])

Flip steps horizontally
红色为分割线,按照橙色线进行数据绿色pair-wise exchange(matrix[i][j], matrix[i][length/2- j] = matrix[i][length/2- j] ,matrix[i][j])

️ 算法实现

Because we only need to flip diagonally and horizontally as written

LeetBook题目

旋转矩阵
给你一幅由 N × N 矩阵表示的图像,其中每个像素的大小为 4 字节.请你设计一种算法,将图像旋转 90 度.不占用额外内存空间能否做到？

实例

给定 matrix =
[
[ 5, 1, 9,11],
[ 2, 4, 8,10],
[13, 3, 6, 7],
[15,14,12,16]
],
原地旋转输入矩阵,使其变为:
[
[15,13, 2, 5],
[14, 3, 4, 1],
[12, 6, 8, 9],
[16, 7,10,11]
]
作者：力扣 (LeetCode)
链接：https://leetcode.cn/leetbook/read/array-and-string/clpgd/
来源：力扣（LeetCode）
著作权归作者所有.商业转载请联系作者获得授权,非商业转载请注明出处.

package com.wpc.leetbook.matrix_;

import org.junit.jupiter.api.Test;

import java.util.Arrays;

public class Solution {
    
    /** * 给你一幅由 N × N 矩阵表示的图像,其中每个像素的大小为 4 字节.请你设计一种算法,将图像旋转 90 度. * 不占用额外内存空间能否做到？ * 思路： * 如果是顺时针旋转90° * It must be flipped diagonally first,再水平翻转 * If it is counterclockwise90° * It must be flipped horizontally first,再对角线翻转 * * @param matrix */
    public void rotate(int[][] matrix) {
    
        //Flip diagonally first
        int length = matrix.length;
        int temp = 0;
        for (int i = 0; i < length; i++) {
    
            for (int j = i + 1; j < length; j++) {
    
                temp = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = temp;
            }
        }
        //在进行水平翻转
        int half_length = matrix.length >> 1;
        int len = length - 1;
        for (int i = 0; i < length; i++) {
    
            for (int j = 0; j < half_length; j++) {
    
                temp = matrix[i][j];
                matrix[i][j] = matrix[i][len - j];
                matrix[i][len - j] = temp;
            }
        }
    }
    @Test
    public void test() {
    
        int[][] matrix = new int[][]{
    {
    5, 1, 9, 11}, {
    2, 4, 8, 10}, {
    13, 3, 6, 7}, {
    15, 14, 12, 16}};
        rotate(matrix);
        System.out.println(Arrays.deepToString(matrix));
    }
}

提交结果

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