Contents.swift

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/*:
 # 旋转矩阵
 
 - 题号：[面试题 01.07](https://leetcode-cn.com/problems/rotate-matrix-lcci/)
 - 难度：中等
 - 描述：
 
     给你一幅由 N × N 矩阵表示的图像，其中每个像素的大小为 4 字节。
     请你设计一种算法，将图像旋转 90 度。
     
     不占用额外内存空间能否做到？
 */

//: ## Code
import Foundation

func rotate(_ matrix: inout [[Int]]) {
    
    // 占用额外空间
    var newMatrix: [[Int]] = []
    
    for _ in matrix {
        newMatrix.append([Int](repeating: 0, count: matrix.count))
    }
    
    for i in 0 ..< matrix.count {
        for j in 0 ..< matrix[i].count {
            newMatrix[j][abs(i - matrix.count + 1)] = matrix[i][j]
        }
    }
    
    matrix = newMatrix
}

func rotate2(_ matrix: inout [[Int]]) {
    
    let n = matrix.count
    
    // 对角线交换
    for i in 0 ..< n {
        for j in i + 1 ..< matrix[i].count {
            (matrix[i][j], matrix[j][i]) = (matrix[j][i], matrix[i][j])
        }
    }
    
    // 每一行以中点进行翻转
    for i in 0 ..< n {
        for j in 0 ..< matrix[i].count >> 1 {
            (matrix[i][j], matrix[i][n - 1 - j]) = (matrix[i][n - 1 - j], matrix[i][j])
        }
    }
}

//: ## Test
var matrix = [
      [1,2,3],
      [4,5,6],
      [7,8,9]
    ]

rotate2(&matrix)

print(matrix)

var matrix2 = [
      [ 5, 1, 9,11],
      [ 2, 4, 8,10],
      [13, 3, 6, 7],
      [15,14,12,16]
    ]

rotate2(&matrix2)

print(matrix2)

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