You are given an n x n 2D matrix representing an image.
Rotate the image by 90 degrees (clockwise).
Note:
You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.
Example 1:
Given input matrix =
[
[1,2,3],
[4,5,6],
[7,8,9]
],
rotate the input matrix in-place such that it becomes:
[
[7,4,1],
[8,5,2],
[9,6,3]
]
Example 2:
Given input matrix =
[
[ 5, 1, 9,11],
[ 2, 4, 8,10],
[13, 3, 6, 7],
[15,14,12,16]
],
rotate the input matrix in-place such that it becomes:
[
[15,13, 2, 5],
[14, 3, 4, 1],
[12, 6, 8, 9],
[16, 7,10,11]
]
Solution:
class Solution {
/*
[1,2,3] [7 8 9] [7 4 1]
[4,5,6] => [4 5 6] => [8 5 2]
[7,8,9] [1 2 3] [9 6 3]
*/
public void rotate(int[][] matrix) {
int n = matrix.length;
if (n == 0) return;
swapByHorizontal(matrix);
swapByBackSlash(matrix);
}
private void swapByBackSlash(int[][] matrix) {
for (int i = 0; i < matrix.length - 1; i ++) {
for (int j = matrix.length - 1; j > i; j --) {
int x = j;
int y = i;
swap(matrix, i, j, x, y);
}
}
}
private void swapByHorizontal(int[][] matrix) {
for (int i = 0; i < matrix.length / 2; i ++) {
int x = matrix.length - 1 - i;
for (int j = 0; j < matrix.length; j ++) {
swap(matrix, i, j, x, j);
}
}
}
private void swap(int[][] matrix, int i, int j, int x, int y) {
int temp = matrix[i][j];
matrix[i][j] = matrix[x][y];
matrix[x][y] = temp;
}
}