Rotate Image @LeetCode

You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Follow up:
Could you do this in-place?

	package leetcode;
	/**
	* Solution: analysis and calculate coordinate.
	* 1. swap lines by mid line
	* 2. swap element by diagonal
	* Don't extract swap function, this is not C/C++!
	*
	* in-place is really head to understand.
	* Reference: http://discuss.leetcode.com/questions/226/rotate-image
	*
	* @author jeffwan
	* @date Apr 2, 2014
	*/
	public class RotateImage {
	// in-place way
	public void rotate(int[][] matrix) {
	if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {
	return;
	}
	int n = matrix.length;
	for (int i = 0; i < n / 2; i++) {
	for (int j = 0; j < (n + 1) / 2; j++) {
	int temp = matrix[i][j];
	matrix[i][j] = matrix[n - j - 1][i];
	matrix[n - j - 1][i] = matrix[n - i - 1][n - j - 1];
	matrix[n - i - 1][n - j - 1] = matrix[j][n - i - 1];
	matrix[j][n - i - 1] = temp;
	}
	}
	}
	public void rotate1(int[][] matrix) {
	if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {
	return;
	}
	int n = matrix.length;
	// turn over along mid line
	for (int i = 0; i < n / 2; i++) {
	for (int j = 0; j < n; j++) {
	int temp = matrix[i][j];
	matrix[i][j] = matrix[n - i - 1][j];
	matrix[n - i - 1][j] = temp;
	}
	}
	// swap along diagonal, only traversal half matrix.
	for (int i = 0; i < n; i++) {
	for (int j = 0; j < i; j++) {
	int temp = matrix[i][j];
	matrix[i][j] = matrix[j][i];
	matrix[j][i] = temp;
	}
	}
	}
	/*
	* Always think brute force way first!
	* Copy to a new matrix, and assign to the original one.
	*/
	public void rotate2(int[][] matrix) {
	if (matrix == null || matrix.length == 0) {
	return;
	}
	int n = matrix.length;
	int[][] newMatrix = new int[n][n];
	for (int i = 0; i < n; i++) {
	for (int j = 0; j < n; j++) {
	newMatrix[i][j] = matrix[n - 1 - j][i];
	}
	}
	for (int i = 0; i < n; i++) {
	for (int j = 0; j < n; j++) {
	matrix[i][j] = newMatrix[i][j];
	}
	}
	}
	}

view raw RotateImage.java hosted with ❤ by GitHub