ocaml: transpose matrix

Author: PoorlyDefinedBehaviour

ocaml/transpose_matrix_dec_10_2023/main.ml

@@ -0,0 +1,59 @@
+(*
+Given a 2D integer array matrix, return the transpose of matrix.
+
+The transpose of a matrix is the matrix flipped over its main diagonal, 
+switching the matrix's row and column indices.
+
+Example 1:
+
+Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]
+Output: [[1,4,7],[2,5,8],[3,6,9]]
+Example 2:
+
+Input: matrix = [[1,2,3],[4,5,6]]
+Output: [
+  [1,4],
+  [2,5],
+  [3,6]]
+ 
+
+Constraints:
+
+m == matrix.length
+n == matrix[i].length
+1 <= m, n <= 1000
+1 <= m * n <= 105
+-109 <= matrix[i][j] <= 109
+*)
+type matrix = int array array 
+[@@deriving show]
+
+(**
+time O(n * m)    
+space O(n * m)
+*)
+let transpose (matrix : matrix) : matrix =
+  let rows = Array.length matrix in
+
+  if rows = 0 then [||]
+  else
+    let columns= Array.length matrix.(0) in 
+    
+    let transposed = Array.init columns (fun _ -> Array.make rows 0) in
+
+    matrix
+    |> Array.iteri (fun i row ->
+        row |> Array.iteri (fun j _ -> 
+        transposed.(j).(i) <- matrix.(i).(j);));
+
+    transposed
+
+let%test_unit "transpose: examples" = 
+  [
+    ([||], [||]);
+    ([|[|1;2;3|];[|4;5;6|];[|7;8;9|]|],[|[|1;4;7|];[|2;5;8|];[|3;6;9|]|]);
+    ([|[|1;2;3|];[|4;5;6|]|], [|[|1;4|];[|2;5|];[|3;6|]|])
+  ] |> 
+  List.iter (fun (matrix, expected) -> 
+    assert (expected = transpose matrix)
+    )