https://leetcode.com/problems/rotate-image/

48. Rotate Image.swift

func flipMatrix(inout matrix: [[Int]]) {
    let n = matrix.count
    for i in 0..<n {
        for j in i+1..<n {
            let temp = matrix[i][j]
            matrix[i][j] = matrix[j][i]
            matrix[j][i] = temp
        }
    }
}

func rotate(inout matrix: [[Int]]) {
    flipMatrix(&matrix)
    let n = matrix.count
    for i in 0..<n {
        for j in 0..<n/2 {
            let temp = matrix[i][j]
            matrix[i][j] = matrix[i][n-j-1]
            matrix[i][n-j-1] = temp
        }
    }
}

var matrix = [[1,2,3],[4,5,6],[7,8,9]]
rotate(&matrix)