Leetcode and Lintcode

Rotate Image

Problem:

You are given an n x n 2D matrix representing an image. Rotate the image by 90 degrees (clockwise).

Example
Given a matrix

[
    [1,2],
    [3,4]
]

rotate it by 90 degrees (clockwise), return

[
    [3,1],
    [4,2]
]

Leetcode link
Lintcode link

Solution:

There are two solutions.
The idea of the first method is to divide the matrix into four smaller matrix, then move each sub-matrix to the rotated position
The idea of the second method is to rotate layer by layer, from the outmost layer to the inner most layer.

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/*************************************************************************
	> File Name: RotatedImage.java
	> Author: Yao Zhang 
	> Mail: psyyz10@163.com 
	> Created Time: Fri 13 Nov 13:56:37 2015
 ************************************************************************/

public class RotatedImage{
	//Solution 1
	public void rotate(int[][] matrix) {
        int length = matrix.length;
        
        for (int i = 0; i < length / 2; i++){
            for (int j = 0; j < (length + 1) / 2; j++){
                int temp = matrix[i][j];
                matrix[i][j] = matrix[length - 1 - j][i];
                matrix[length - 1 - j][i] = matrix[length - 1 - i][length - 1 - j];
                matrix[length - 1 - i][length - 1 - j] = matrix[j][length - 1 - i];
                matrix[j][length - 1 - i] = temp;
            }
        }
    }

    //Solution 2
    public void rotate(int[][] matrix) {
        int length = matrix.length;
        
        for (int layer = 0; layer < length / 2; layer++){
            int last = length - 1 - layer;
            for (int j = layer; j < last; j++){
                int offset = j - layer;
                int temp = matrix[layer][j];
                matrix[layer][j] = matrix[last - offset][layer];
                matrix[last - offset][layer] = matrix[last][last - offset];
                matrix[last][last - offset] = matrix[j][last];
                matrix[j][last] = temp;
            }
        }
    }
}