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Copy pathrotateImage.java
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53 lines (36 loc) · 1.83 KB
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/*
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]]
Constraints:
n == matrix.length == matrix[i].length
1 <= n <= 20
-1000 <= matrix[i][j] <= 1000
*/
//when looking for a pattern, we notice that there numbers in groups of four that change positions with one another
//approach: find the positions of those four and swamp them with their right neighbor to make the 90 degree turn
class Solution {
public void rotate(int[][] matrix) {
int n = matrix.length; //given
//adding one and dividing with int division accounts for both odd and even length of n
for (int i = 0; i < ((n + 1) / 2); i ++) {
for (int j = 0; j < (n / 2); j++) {
//Starts with far edges and works its way back to the left
//hold first of group, use to replace in final swap
int temp = matrix[n - j - 1][i];
//keep replacing with group member on next side of the square
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] = matrix[i][j];
//finally replace last spot with first spot held in temp
matrix[i][j] = temp;
//move to next group with index incrementation
}
}
}
}