func rotate(_ matrix: inout [[Int]]) {

var left = 0, right = matrix.count - 1

while left < right {

for i in 0...right-left-1 {

let top = left, bottom = right

// save the topLeft

let topLeft = matrix[top][left + i]

// move bottom left into top left

matrix[top][left + i] = matrix[bottom - i][left]

// move bottom right into bottom left

matrix[bottom - i][left] = matrix[bottom][right - i]

// move top right into bottom right

matrix[bottom][right - i] = matrix[top + i][right]

// move top left into top right

matrix[top + i][right] = topLeft

}

right -= 1

left += 1

}

}