Leetcode T48: rotating images

Title Description

Given a n × n Two dimensional matrix of matrix Represents an image . Please rotate the image clockwise 90 degree .

You must be there. In situ Rotated image , This means that you need to modify the input two-dimensional matrix directly . Please do not Use another matrix to rotate the image .

Example 1：

Input ：matrix = [[1,2,3],[4,5,6],[7,8,9]]
Output ：[[7,4,1],[8,5,2],[9,6,3]]

Example 2：

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]]

Tips ：

• n == matrix.length == matrix[i].length
• 1 <= n <= 20
• -1000 <= matrix[i][j] <= 1000

Ideas

rotate 90° Equal to first Transposition , Again Mirror symmetry .

Code

    public void rotate(int[][] matrix) {
    
    	int n = matrix.length;
    	//  Transposition 
    	for(int i = 0; i < n; i++) {
    
    		for(int j = 0; j < i; j++) {
    
    			int t = matrix[i][j]; matrix[i][j] = matrix[j][i]; matrix[j][i] = t;
    		}
    	}
    	//  Mirror symmetry 
    	for(int i = 0; i < n; i++) {
    
    		for(int j = 0; j < n/2; j++) {
    
    			int t = matrix[i][j]; matrix[i][j] = matrix[i][n-1-j]; matrix[i][n-1-j] = t;
    		}
    	}
    }