LeetCode-in-All

48. Rotate Image

Medium

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

# @param {Integer[][]} matrix
# @return {Void} Do not return anything, modify matrix in-place instead.
def rotate(matrix)
  n = matrix.length
  (0...n / 2).each do |i|
    (i...(n - i - 1)).each do |j|
      pos = [[i, j], [j, n - 1 - i], [n - 1 - i, n - 1 - j], [n - 1 - j, i]]
      t = matrix[pos[0][0]][pos[0][1]]
      (1...pos.length).each do |k|
        temp = matrix[pos[k][0]][pos[k][1]]
        matrix[pos[k][0]][pos[k][1]] = t
        t = temp
      end
      matrix[pos[0][0]][pos[0][1]] = t
    end
  end
end

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