(LeetCode) 48. Rotate Image

Rotate Image

• Explore : Interview > Top Interveiw Questions > Easy Collection
• 분류 : Array
• 난이도 : Medium

Problem

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

Solution

Exapnder

class Solution {
    fun rotate(matrix: Array<IntArray>): Unit {
        matrix.reverse()
        for (i in matrix.indices) {
            for (j in i + 1 until  matrix[i].size) {
                matrix[i][j] = matrix[j][i].also {
                    matrix[j][i] = matrix[i][j]
                }
            }
        }
    }
}

Point of Thinking

• 시계방향으로 회전하는 방법은 여러가지가 있다.
  • 행렬 회전 연산을 써보려고 했으나 배보다 배꼽이 더 큼.
  • 회전 기준점을 잡고 swap하는 것으로 해결