diff --git a/2023/day21.py b/2023/day21.py
new file mode 100755
index 0000000..df91efe
--- /dev/null
+++ b/2023/day21.py
@@ -0,0 +1,88 @@
+#!/usr/bin/python3
+"""
+Jour 21 du défi Advent Of Code pour l'année 2023
+"""
+import os
+from tqdm import tqdm
+
+def read_sample():
+    """récupère les entrées depuis le fichier texte correspondant"""
+    filename = os.path.join(os.path.dirname(__file__ ), "inputs", "day21.txt")
+    with open(filename, 'r') as f:
+        sample = f.read().split('\n')
+    sample = [[j for j in i] for i in sample if i != '' ]
+    return sample
+
+def do_steps(sample, steps=26501365, ext=False):
+    len_sample = len(sample)
+    len_sample0 = len(sample[0])
+
+    def find_S():
+        for i in range(len_sample):
+            for j in range(len_sample0):
+                if sample[i][j] == 'S':
+                    return (i, j)
+
+    def valid(pos):
+        return pos[0] >= 0 and pos[1] >= 0 and pos[0] < len_sample and pos[1] < len_sample0
+
+
+    def is_point(pos, ext=False):
+        if not ext and valid(pos):
+            if sample[pos[0]][pos[1]] == '.' or sample[pos[0]][pos[1]] == 'S':
+                return True
+            return False
+        if ext and sample[pos[0]%len_sample][pos[1]%len_sample0] == '.' or sample[pos[0]%len_sample][pos[1]%len_sample0] == 'S':
+            return True
+        return False
+
+    def voisins(pos, ext=False):
+        i, j = pos
+        v = []
+        if valid((i, j-1)) and is_point((i, j-1), ext=ext):
+            v.append((i, j-1))
+        if valid((i-1, j)) and is_point((i-1, j), ext=ext):
+            v.append((i-1, j))
+        if valid((i, j+1)) and is_point((i, j+1), ext=ext):
+            v.append((i, j+1))
+        if valid((i+1, j)) and is_point((i+1, j), ext=ext):
+            v.append((i+1, j))
+        return v
+
+    i, j = find_S()
+    pos_ts = {(i, j): [(0, 0)]}
+    for i in tqdm(range(steps)):
+        new_pos_ts = {}
+        for pos in pos_ts.keys():
+            for p in voisins(pos, ext=ext):
+                mp = (p[0]%len_sample, p[1]%len_sample0)
+                tile = (p[0]//len_sample, p[1]//len_sample0)
+                if mp not in new_pos_ts.keys():
+                    new_pos_ts[mp] = []
+                for elem in pos_ts[pos]:
+                    t = (tile[0]+elem[0], tile[1]+elem[1])
+                    if t not in new_pos_ts[mp]:
+                        new_pos_ts[mp].append(t)
+
+        pos_ts = new_pos_ts
+    return pos_ts
+
+
+def part1(sample):
+    """Partie 1 du défi"""
+    return sum([len(i) for i in do_steps(sample, steps=64, ext=False).values()])
+
+def part2(sample):
+    """Partie 2 du défi"""
+    print("WARNING, this will take a lot of time (and could not even work)")
+    return sum([len(i) for i in do_steps(sample, ext=True).values()])
+
+
+def main():
+    """Fonction principale"""
+    sample = read_sample()
+    print(f"part1: {part1(sample)}")
+    print(f"part2: {part2(sample)}")
+
+if __name__ == "__main__":
+    main()
\ No newline at end of file