g0001_0100.s0048_rotate_image.Solution Maven / Gradle / Ivy

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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0001_0100.s0048_rotate_image;

// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Array #Math #Matrix
// #Data_Structure_II_Day_3_Array #Programming_Skills_II_Day_7 #Udemy_2D_Arrays/Matrix
// #Big_O_Time_O(n^2)_Space_O(1) #2023_08_11_Time_0_ms_(100.00%)_Space_41.5_MB_(34.96%)

/**
 * 48 - Rotate Image\.
 *
 * Medium
 *
 * You are given an `n x n` 2D `matrix` representing an image, rotate the image by **90** degrees (clockwise).
 *
 * 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.
 *
 * **Example 1:**
 *
 * ![](https://assets.leetcode.com/uploads/2020/08/28/mat1.jpg)
 *
 * **Input:** matrix = \[\[1,2,3],[4,5,6],[7,8,9]]
 *
 * **Output:** [[7,4,1],[8,5,2],[9,6,3]] 
 *
 * **Example 2:**
 *
 * ![](https://assets.leetcode.com/uploads/2020/08/28/mat2.jpg)
 *
 * **Input:** matrix = \[\[5,1,9,11],[2,4,8,10],[13,3,6,7],[15,14,12,16]]
 *
 * **Output:** [[15,13,2,5],[14,3,4,1],[12,6,8,9],[16,7,10,11]] 
 *
 * **Example 3:**
 *
 * **Input:** matrix = \[\[1]]
 *
 * **Output:** [[1]] 
 *
 * **Example 4:**
 *
 * **Input:** matrix = \[\[1,2],[3,4]]
 *
 * **Output:** [[3,1],[4,2]] 
 *
 * **Constraints:**
 *
 * *   `matrix.length == n`
 * *   `matrix[i].length == n`
 * *   `1 <= n <= 20`
 * *   `-1000 <= matrix[i][j] <= 1000`
**/
public class Solution {
    public void rotate(int[][] matrix) {
        int n = matrix.length;
        for (int i = 0; i < n / 2; i++) {
            for (int j = i; j < n - i - 1; j++) {
                int[][] pos =
                        new int[][] {
                            {i, j}, {j, n - 1 - i}, {n - 1 - i, n - 1 - j}, {n - 1 - j, i}
                        };
                int t = matrix[pos[0][0]][pos[0][1]];
                for (int k = 1; k < pos.length; k++) {
                    int temp = matrix[pos[k][0]][pos[k][1]];
                    matrix[pos[k][0]][pos[k][1]] = t;
                    t = temp;
                }
                matrix[pos[0][0]][pos[0][1]] = t;
            }
        }
    }
}