spiralTo2D.swift

/// Input - [1, 2, 3, 6, 9, 8, 7, 4, 5], m = 3, n = 3
func spiralTo2DMatrix(_ arr: [Int], row: Int, col: Int) -> [[Int]] {
    /// Base condition
    var result:[[Int]] = [[Int]]()
    guard  arr.isEmpty == false else { return result }
    /// Logic
    for _ in 0..<row {
        result.append(Array(repeating: 0, count: col))
    }
    
    var r1 = 0, c1 = 0
    var r2 = row - 1, c2 = col - 1
    var i = 0
     while r1 <= r2 && c1 <= c2 {
            /// Go from c1 to c2 and append the element
            for c in stride(from: c1, through: c2, by: 1) {
                result[r1][c] = arr[i]
                i = i + 1
                 /// 1,2,3
            }
            /// Go from next row till endof row
            for r in stride(from: r1 + 1, through: r2, by: 1) {
                result[r][c2] = arr[i]
                i = i + 1
            }
            
            if r1 < r2 && c1 < c2 {
                /// Move from c2-1 till c1
                for c in stride(from: c2 - 1, through: c1, by: -1) {
                    result[r2][c] = arr[i]
                    i = i + 1
                }
                /// Move from r2-1 till r1
                for r in stride(from: r2 - 1, to: r1, by: -1) {
                    result[r][c1] = arr[i]
                    i = i + 1
                }
            }
            r1 = r1 + 1
            r2 = r2 - 1
            c1 = c1 + 1
            c2 = c2 - 1
        }
    return result
}
let flatInput = [1, 2, 3, 6, 9, 8, 7, 4, 5]
let newInput = [1, 2, 3, 4, 5, 6, 12, 18, 17, 16, 15, 14, 13, 7, 8, 9, 10, 11]
let m = 3, n = 3
let spiralMatrix = spiralTo2DMatrix(newInput, row: 3, col: 6)
print(spiralMatrix)