diff --git a/exercises/ex04/ex04a.py b/exercises/ex04/ex04a.py
new file mode 100644
index 0000000..28a292c
--- /dev/null
+++ b/exercises/ex04/ex04a.py
@@ -0,0 +1,11 @@
+def add(ls):
+    if len(ls) > 0:
+        ls = list(map(lambda x: str(x), ls))
+        ls[-1] = f"and {ls[-1]}"
+        print(", ".join(ls))
+    else:
+        print("")
+
+
+add([0, 1, 2, 3])
+add([])
diff --git a/exercises/ex04/ex04b.py b/exercises/ex04/ex04b.py
new file mode 100644
index 0000000..513b90e
--- /dev/null
+++ b/exercises/ex04/ex04b.py
@@ -0,0 +1,40 @@
+import random
+
+
+def flip(times):
+    res = []
+    for i in range(times):
+        res.append(random.choice(["H", "T"]))
+    return res
+
+
+def check(flips, reps, streaks):
+    last, h, t = "", 0, 0
+    for f in flips:
+        if last == f:
+            if f == "H":
+                h += 1
+            else:
+                t += 1
+        else:
+            h = 0
+            t = 0
+        if h == reps or t == reps:
+            streaks += 1
+            break
+        last = f
+    return streaks
+
+
+def test(times, length=100, reps=6):
+    streaks = 0
+    for i in range(times):
+        print(f"Testing {int((i * 100) / times)}%")
+        streaks = check(flip(length), reps, streaks)
+    print(f"Streak length: {reps}")
+    print(f"Flips length: {length}")
+    print(f"Tests: {times}")
+    print(f"Result: {streaks} streaks ({(streaks * 100) / times}%).")
+
+
+test(10000, reps=6)
diff --git a/exercises/ex04/ex04c.py b/exercises/ex04/ex04c.py
new file mode 100644
index 0000000..886b7fc
--- /dev/null
+++ b/exercises/ex04/ex04c.py
@@ -0,0 +1,33 @@
+grid = [
+    [".", ".", ".", ".", ".", "."],
+    [".", "0", "0", ".", ".", "."],
+    ["0", "0", "0", "0", ".", "."],
+    ["0", "0", "0", "0", "0", "."],
+    [".", "0", "0", "0", "0", "0"],
+    ["0", "0", "0", "0", "0", "."],
+    ["0", "0", "0", "0", ".", "."],
+    [".", "0", "0", ".", ".", "."],
+    [".", ".", ".", ".", ".", "."],
+]
+
+
+def show(grid):
+    for row in grid:
+        print("".join(row))
+    print("")
+
+
+def reorder(grid):
+    res, curr = [], 0
+    while curr < len(grid[0]):
+        line = ""
+        for row in grid:
+            line += row[curr]
+        res.append(list(line))
+        curr += 1
+    return res
+
+
+show(grid)
+grid = reorder(grid)
+show(grid)