Question Definition
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]
]
My Java Solution
class Solution {
public void rotate(int[][] matrix) {
rotate(matrix, 0, 0, matrix.length);
}
private void rotate(int[][] matrix, int startX, int startY, int length){
if(length == 1) return;
for(int i = 0; i < length / 2; i++){
for(int j = 0; j < length / 2; j++){
int temp = matrix[startX + i][startY + j];
matrix[startX + i][startY + j] = matrix[startX + length - length / 2 + i][startY + j];
matrix[startX + length - length / 2 + i][startY + j] = matrix[startX + length - length / 2 + i][startY + length - length / 2 + j];
matrix[startX + length - length / 2 + i][startY + length - length / 2 + j] = matrix[startX + i][startY + length - length / 2 + j];
matrix[startX + i][startY + length - length / 2 + j] = temp;
}
}
if(length % 2 != 0){
for(int i = 0; i < length / 2; i++){
int temp = matrix[startX + i][startY + length / 2];
matrix[startX + i][startY + length / 2] = matrix[startX + length / 2][startY + i];
matrix[startX + length / 2][startY + i] = matrix[startX + length - i - 1][startY + length / 2];
matrix[startX + length - i - 1][startY + length / 2] = matrix[startX + length / 2][startY + length - i - 1];
matrix[startX + length / 2][startY + length - i - 1] = temp;
}
}
if(length > 3){
rotate(matrix, startX, startY, length / 2);
rotate(matrix, startX + length - length / 2, startY, length / 2);
rotate(matrix, startX, startY + length - length / 2, length / 2);
rotate(matrix, startX + length - length / 2, startY + length - length / 2, length / 2);
}
}
}
Best Java Solution
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 - 1 - i; ++j) {
int tmp = matrix[i][j];
matrix[i][j] = matrix[n - 1 - j][i];
matrix[n - 1 - j][i] = matrix[n - 1 - i][n - 1 - j];
matrix[n - 1 - i][n - 1 - j] = matrix[j][n - 1 - i];
matrix[j][n - 1 - i] = tmp;
}
}
}
}
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