problems(js): add “2625. Flatten Deeply Nested Array”

Signed-off-by: Matej Focko <mfocko@redhat.com>

problems/js/flatten-deeply-nested-array.js

@@ -0,0 +1,34 @@
+/**
+ * @param {any[]} arr
+ * @param {number} depth
+ * @return {any[]}
+ */
+var flat = function (arr, n) {
+    let stack = [[arr, 0, 0]];
+
+    let flattened = [];
+    while (stack.length) {
+        let [arr, depth, i] = stack.pop();
+        if (i >= arr.length) {
+            // finished with the nested array
+            continue;
+        }
+
+        // if it's a nested array and not deep enough
+        if (depth < n && arr[i] instanceof Array) {
+            // gotta continue with the next element of the array
+            stack.push([arr, depth, i + 1]);
+
+            // gotta start with the first element of the nested
+            stack.push([arr[i], depth + 1, 0]);
+
+            // yielding is done only on the elements themselves
+            continue;
+        }
+
+        flattened.push(arr[i]);
+        stack.push([arr, depth, i + 1]);
+    }
+
+    return flattened;
+};