we can iterate just once!

04/index.ts

@@ -17,16 +17,12 @@ console.log(
     .reduce(
       (coll, curr, index, array) => {
         // 2D string matching is a pain. Let's turn it into a 1D problem!
-        // create the columns
         curr.split("").forEach((s, i) => {
+          // create the columns
           coll[i] += s;
-        });
-        // create the down-left-diagonals
-        curr.split("").forEach((s, i) => {
-          coll[i + array.length + index] += s;
-        });
-        // create the down-right-diagonals
-        curr.split("").forEach((s, i) => {
+          // create the left-diagonals
+          coll[array.length + index + i] += s;
+          // create the right-diagonals
           coll[array.length * 4 + index - i - 2] += s;
         });
         // include the original row