55 lines
1.9 KiB
Java
55 lines
1.9 KiB
Java
package matrix;
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/**
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* 题目：48. 旋转图像 (setZeroes)
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* 描述：给定一个 n × n 的二维矩阵 matrix 表示一个图像。请你将图像顺时针旋转 90 度。
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* 你必须在 原地 旋转图像，这意味着你需要直接修改输入的二维矩阵。请不要 使用另一个矩阵来旋转图像。
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* 链接：https://leetcode.cn/problems/rotate-image/description/
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*
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示例 1:
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输入：matrix = [[1,2,3],[4,5,6],[7,8,9]]
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输出：[[7,4,1],[8,5,2],[9,6,3]]
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示例 2:
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输入：matrix = [[5,1,9,11],[2,4,8,10],[13,3,6,7],[15,14,12,16]]
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输出：[[15,13,2,5],[14,3,4,1],[12,6,8,9],[16,7,10,11]]
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*/
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//不会原地旋转，只会借助辅助数组
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public class RotateImage {
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public void rotate(int[][] matrix) {
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int n = matrix.length;
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int[][] matrix_new = new int[n][n];
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for (int i = 0; i < n; ++i) {
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for (int j = 0; j < n; ++j) {
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matrix_new[j][n - i - 1] = matrix[i][j];
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}
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}
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for (int i = 0; i < n; ++i) {
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for (int j = 0; j < n; ++j) {
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matrix[i][j] = matrix_new[i][j];
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}
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}
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}
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//原地旋转， (i,j)->(j,n-i-1) == 先翻转(j,i)->再交换左右列(j,n-i-1)
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public void rotate1(int[][] matrix) {
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int n = matrix.length;
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// 1. 转置矩阵：行列互换
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for (int i = 0; i < n; i++) {
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// j 从 i+1 开始，避免重复交换
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for (int j = i + 1; j < n; j++) {
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int temp = matrix[i][j];
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matrix[i][j] = matrix[j][i];
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matrix[j][i] = temp;
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}
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}
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// 2. 翻转每一行：相当于水平翻转
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for (int i = 0; i < n; i++) {
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for (int j = 0; j < n / 2; j++) {
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int temp = matrix[i][j];
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matrix[i][j] = matrix[i][n - 1 - j];
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matrix[i][n - 1 - j] = temp;
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}
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}
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}
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}
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