You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise).
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:
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]]
Example 3:
Input: matrix = [[1]]
Output: [[1]]
Example 4:
Input: matrix = [[1,2],[3,4]]
Output: [[3,1],[4,2]]
Constraints:
- matrix.length == n
- matrix[i].length == n
- 1 <= n <= 20
- -1000 <= matrix[i][j] <= 1000
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 temp = 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] = temp;
}
}
}
}class Solution {
/*
You are given an n x n 2D matrix representing an image, rotate the image by 90 degrees (clockwise).
Iterate the an outer grid from the following points and directions:
-Top Left Corner -> Top Right
-Top Right Corner -> Bottom Right
-Bottom Right Corner -> Bottom Left Corner
-Bottom Left Corner -> Top Left Corner
It'll take three swaps to get every element in the right place
*/
private int[][] m = null;
public void rotate(int[][] matrix){
m = matrix;
//outer-square/inner-square iterator
for(int i = 0; i < matrix.length / 2; i++){
int boundary = matrix.length - ( i + 1 );
int topLeftY = i;
int topLeftX = i;
int topRightY = i;
int topRightX = boundary;
int botRightY = boundary;
int botRightX = boundary;
int botLeftY = boundary;
int botLeftX = i;
for(int j = i; j < boundary; j++){
swap(topLeftY, topLeftX, topRightY, topRightX);
swap(botLeftY, botLeftX, topLeftY, topLeftX);
swap(botRightY, botRightX, botLeftY, botLeftX);
topLeftX++;
topRightY++;
botRightX--;
botLeftY--;
}
}
}
private void swap(int i1, int i2, int j1, int j2){
int temp = m[i1][i2];
m[i1][i2] = m[j1][j2];
m[j1][j2] = temp;
}
}