diff --git a/2020/day06/bash.sh b/2020/day06/bash.sh
deleted file mode 100755
index 4cdc037..0000000
--- a/2020/day06/bash.sh
+++ /dev/null
@@ -1,4 +0,0 @@
-#! /bin/bash
-PATH=.:$PATH
-IN="$1"
-time { ex1.bash < $IN; ex2.bash < $IN; } 2>&1
diff --git a/2020/day06/c.sh b/2020/day06/c.sh
deleted file mode 100755
index 0b5bd2d..0000000
--- a/2020/day06/c.sh
+++ /dev/null
@@ -1,5 +0,0 @@
-#! /bin/bash
-PATH=.:$PATH
-IN="$1"
-echo IN=$IN
-time for i in ex1-c ex2-c; do "$i" < "$IN"; done 2>&1
diff --git a/2020/day22/aoc-c.c b/2020/day22/aoc-c.c
index 8b7bd5b..880587e 100644
--- a/2020/day22/aoc-c.c
+++ b/2020/day22/aoc-c.c
@@ -1,46 +1,212 @@
 /* aoc-c.c: Advent2020, day 22, part 1
  */
 
+#include <ctype.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
-#include <ctype.h>
 
+#include "debug.h"
+#include "hashtable.h"
 #include "list.h"
 #include "pool.h"
-#include "debug.h"
 
-struct card {
-    int card;
-    struct list_head list;
-};
+typedef struct card {
+    u8 card;               /* card value */
+    struct list_head list; /* list of cards */
+} card_t;
 
-struct player {
-    int ncards;
-    struct list_head head;
-} players[2];
+typedef struct player {
+    int ncards;            /* player cards # */
+    struct list_head head; /* head of cards list */
+} player_t;
+
+/* zobrist hash used to find duplicate positions
+ */
+typedef struct hash {
+    u32 zobrist;
+    struct list_head players[2];
+    struct hlist_node hlist;
+} hash_t;
+
+#define HBITS 10 /* 10 bits: hash size is 1024 */
+#define CARDS 50
 
 pool_t *pool_cards;
+pool_t *pool_hash;
+static u32 zobrist_table[2][CARDS][CARDS];
 
-static void print_cards()
+static void zobrist_init()
+{
+    for (int i = 0; i < 2; ++i)
+        for (int j = 0; j < 50; ++j)
+            for (int k = 0; k < 50; ++k)
+                zobrist_table[i][j][k] = rand();
+}
+
+static u32 zobrist(player_t *players)
+{
+    u32 zobrist = 0;
+    card_t *card;
+
+    for (int p = 0; p < 2; ++p) {
+        int pos = 0;
+        list_for_each_entry(card, &players[p].head, list) {
+            zobrist ^= zobrist_table[p][pos][card->card - 1];
+            pos++;
+        }
+    }
+    return zobrist;
+}
+
+static __always_inline u32 hash(u32 h)
+{
+    return hash_32(h, HBITS);
+}
+
+static void print_cards(player_t *players)
 {
     struct card *card;
+
     for (int player = 0; player < 2; ++player) {
-        log(2, "player %d (%d cards): ", player + 1, players[player].ncards);
+        int c = 0;
+        log(2, "Player %d's deck: ", player + 1);
         list_for_each_entry(card, &players[player].head, list) {
-            log(2, "%d ", card->card);
+            if (c++)
+                log(2, ",");
+            log(2, " %d", card->card);
         }
         log(2, "\n");
     }
 }
 
-static void parse()
+static int equal_decks(hash_t *hasht, player_t *new)
+{
+    //int i = 0;
+    for (int i = 0; i < 2; ++i) {
+        card_t *c1 = list_first_entry_or_null(&hasht->players[i], card_t, list);
+        card_t *c2 = list_first_entry_or_null(&new[i].head, card_t, list);
+        log_f(3, "p=%d c1=%p c2=%p", i + 1, c1, c2);
+
+        if (!c1 || !c2) {
+        /* one list is empty and one is not */
+        //if ((!c1 && c2) || (c1 && !c2)) {
+            log(3, "NULL\n");
+            return 0;
+        }
+        log_f(3, "\nplayer=%d ", i + 1);
+
+        while (!list_entry_is_head(c1, &hasht->players[i], list) &&
+               !list_entry_is_head(c2, &new[i].head, list) &&
+               c1->card == c2->card) {
+            log(3, "c1=%d c2=%d ", c1->card, c2->card);
+            if (c1->card != c2->card) {
+                log(3, "\n");
+                return 0;
+            }
+            c1 = list_next_entry(c1, list);
+            c2 = list_next_entry(c2, list);
+        }
+        log(3, "\nd1=%p c1=%p/%d\nd2=%p c2=%p/%d ",
+            &hasht[i], c1, list_entry_is_head(c1, &hasht->players[i], list),
+            &new[i], c2, list_entry_is_head(c2, &new[i].head, list));
+        //log(3, "\nZOBI\n");
+        if (!list_entry_is_head(c1, &hasht->players[i], list) ||
+            !list_entry_is_head(c2, &new[i].head, list))
+            return 0;
+        log(3, "\n");
+        //log(3, "\nZOBI\n");
+    }
+    return 1;
+}
+
+static hash_t *create_hash(player_t *players, u32 h)
+{
+    struct card *card;
+    hash_t *hash = pool_get(pool_hash);
+    INIT_HLIST_NODE(&hash->hlist);
+    hash->zobrist = h;
+
+    for (int i = 0; i < 2; ++i) {
+        log_f(4, "player %d: ", i + 1);
+        INIT_LIST_HEAD(&hash->players[i]);
+        list_for_each_entry(card, &players[i].head, list) {
+            struct card *new = pool_get(pool_cards);
+            new->card = card->card;
+            list_add_tail(&new->list, &hash->players[i]);
+            log(4, "%d ", card->card);
+        }
+        log(4, "\n");
+    }
+    log_f(3, "hash=%p p1-next=%p p2-next=%p\n", hash,
+          hash->players[0].next, hash->players[1].next);
+    for (int i = 0; i < 2; ++i) {
+        log_f(4, "duped player %d: ", i + 1);
+        list_for_each_entry(card, &hash->players[i], list) {
+            log(4, "%d ", card->card);
+        }
+        log(4, "\n");
+    }
+    return hash;
+}
+
+static player_t *create_subgame(player_t *from, player_t *to)
+{
+    struct card *card;
+
+    for (int i = 0; i < 2; ++i) {
+        int n = 0, ncards;
+
+        to[i].ncards = from[i].ncards - 1;
+        INIT_LIST_HEAD(&to[i].head);
+        list_for_each_entry(card, &from[i].head, list) {
+            if (!n) {
+                to[i].ncards = ncards = card->card;
+            } else {
+                struct card *new = pool_get(pool_cards);
+                new->card = card->card;
+                list_add_tail(&new->list, &to[i].head);
+                log(4, "%d ", card->card);
+                if (!--ncards)
+                    break;
+            }
+            n++;
+        }
+    }
+    return to;
+}
+
+/**
+ * find_deck - find deck in an hashtable bucket
+ */
+static hash_t *find_deck(struct hlist_head *hasht, player_t *players)
+{
+    hash_t *cur;
+    u32 z = zobrist(players);
+    u32 h = hash(z);
+    log_f(3, "zobrist = %u/%u ", z, h);
+    hlist_for_each_entry(cur, hasht + h, hlist) {
+        log(3, "[%u]\n", cur->zobrist);
+        if (cur->zobrist == z && equal_decks(cur, players)) {
+            // && equal_decks(&cur->players[1], &players[1].head)) {
+            log_f(3, "found\n");
+            return cur;
+        }
+    }
+    log_f(3, "not found\n");
+    cur = create_hash(players, z);
+    hlist_add_head(&cur->hlist, &hasht[h]);
+    return NULL;
+}
+
+
+static player_t *parse(player_t *players)
 {
     size_t alloc;
     ssize_t len;
     char *buf = NULL;
-    int player = -1;
+    int player = 0;
     struct card *card;
 
     INIT_LIST_HEAD(&players[0].head);
@@ -48,12 +214,11 @@ static void parse()
     players[0].ncards = players[1].ncards = 0;
     while ((len = getline(&buf, &alloc, stdin)) > 0) {
         buf[--len] = 0;
-        if (len == 0)
-            continue;
-        if (*buf == 'P') {
+        if (len == 0) {
             player++;
             continue;
-        } else if (isdigit(*buf)) {               /* card */
+        }
+        if (isdigit(*buf)) { /* card */
             card = pool_get(pool_cards);
             card->card = atoi(buf);
             players[player].ncards++;
@@ -61,6 +226,7 @@ static void parse()
         }
     }
     free(buf);
+    return players;
 }
 
 static int usage(char *prg)
@@ -69,46 +235,93 @@ static int usage(char *prg)
     return 1;
 }
 
-static long part1()
+static void winmove(player_t *winner, player_t *loser)
 {
-    struct card *c1, *c2;
-    int round = 0, mult = 1;
-    long res = 0;
+    card_t *win, *lose;
+
+    win = list_first_entry(&winner->head, struct card, list);
+    lose = list_first_entry(&loser->head, struct card, list);
+    list_move_tail(&win->list, &winner->head);
+    list_move_tail(&lose->list, &winner->head);
+    loser->ncards--;
+    winner->ncards++;
+}
+
+static long part1(player_t *players)
+{
+    int round = 0, winner = 0;
 
     while (players[0].ncards > 0 && players[1].ncards > 0) {
-        c1 = list_first_entry_or_null(&players[0].head, struct card, list);
-        c2 = list_first_entry_or_null(&players[1].head, struct card, list);
-        if (c1->card > c2->card) {
-            list_move_tail(&c1->list, &players[0].head);
-            list_move_tail(&c2->list, &players[0].head);
-            players[1].ncards--;
-            players[0].ncards++;
-        } else {
-            list_move_tail(&c2->list, &players[1].head);
-            list_move_tail(&c1->list, &players[1].head);
-            players[0].ncards--;
-            players[1].ncards++;
-        }
+        winner = 0;
+        /*  we can use list_first_entry() macro, as both lists are not empty */
+        int val1 = list_first_entry(&players[0].head, struct card, list)->card;
+        int val2 = list_first_entry(&players[1].head, struct card, list)->card;
+        if (val2 > val1)
+            winner = 1;
+        winmove(players + winner, players + 1 - winner);
         round++;
-        log(2, "\nafter round %d\n", round);
-        print_cards();
     }
-    list_for_each_entry_reverse(c1,
-                                players[0].ncards? &players[0].head: &players[1].head,
-                                list) {
-        res += c1->card * mult++;
-    };
-    return res;
+
+    return winner;
 }
 
-static long part2()
+static long part2(player_t *players)
 {
-    return 2;
+    int round = 1, winner = 0, game;
+    static int maxgame = 0;
+    DEFINE_HASHTABLE(hasht_deck, HBITS); /* htable for dup decks */
+
+    log(2, "=== Game %d ===\n", game = ++maxgame);
+    while (players[0].ncards > 0 && players[1].ncards > 0) {
+        int val1, val2;
+        winner = 0;
+
+        log(2, "\n-- Round %d (Game %d) --\n", round, game);
+        print_cards(players);
+
+        if (find_deck(hasht_deck, players)) {
+            log(3, "dup found\n");
+            goto end; // return winner;
+        } else {
+            log(3, "dup not found\n");
+        }
+
+        /*  we can use list_first_entry() macro, as both lists are not empty */
+        val1 = list_first_entry(&players[0].head, struct card, list)->card;
+        val2 = list_first_entry(&players[1].head, struct card, list)->card;
+        log(2, "Player 1 plays: %d\n", val1);
+        log(2, "Player 2 plays: %d\n", val2);
+
+        if (players[0].ncards > val1 && players[1].ncards > val2) {
+            player_t sub[2];
+            log(2, "Playing a sub-game to determine the winner...\n\n");
+            winner = part2(create_subgame(players, sub));
+            log(2, "\n...anyway, back to game %d\n", game);
+        } else {
+            if (val2 > val1)
+                winner = 1;
+        }
+        winmove(players + winner, players + 1 - winner);
+        log(2, "Player %d wins round %d of game %d!\n", winner + 1, round, game);
+
+        round++;
+    }
+end:
+    log(2, "The winner of game %d is player %d!\n", game, winner + 1);
+    /*  cleanup decks */
+    card_t *card, *tmp;
+    if (game != 1) {
+        for (int i = 0; i < 2; ++i) {
+            list_for_each_entry_safe(card, tmp, &players[i].head, list) {
+                list_del(&card->list);
+                pool_add(pool_cards, card);
+            }
+        }
+    }
+    return winner;
 }
 
-int main(ac, av)
-    int ac;
-    char **av;
+int main(int ac, char **av)
 {
     int opt, part = 1;
 
@@ -117,18 +330,35 @@ int main(ac, av)
             case 'd':
                 debug_level_set(atoi(optarg));
                 break;
-            case 'p':                             /* 1 or 2 */
+            case 'p': /* 1 or 2 */
                 part = atoi(optarg);
                 if (part < 1 || part > 2)
-            default:
+                default:
                     return usage(*av);
         }
     }
 
     pool_cards = pool_create("cards", 128, sizeof(struct card));
+    pool_hash = pool_create("hash", 128, sizeof(struct hash));
+    zobrist_init();
+    player_t players[2];
+    parse(players);
 
-    parse();
-    print_cards();
-    printf("%s : res=%ld\n", *av, part == 1? part1(): part2());
-    exit (0);
+    if (part == 1)
+        part1(players);
+    else
+        part2(players);
+
+    /* we don't need to check for winner, as one list is empty */
+    log(2, "\n== Post-game results ==\n");
+    print_cards(players);
+    card_t *card;
+    long res = 0, mult = 1;
+    list_for_each_entry_reverse(card, &players[0].head, list)
+        res += card->card * mult++;
+    list_for_each_entry_reverse(card, &players[1].head, list)
+        res += card->card * mult++;
+
+    printf("%s : res=%ld\n", *av, res);
+    exit(0);
 }