(LeetCode) Rotate Image

Rotate Image

  • 분류 : Array
  • 난이도 : Easy

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

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Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]
Output: [[7,4,1],[8,5,2],[9,6,3]]

Example 2

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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

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Input: matrix = [[1]]
Output: [[1]]

Example 4

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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
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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