diff --git a/day16/Makefile b/day16/Makefile
index 211cf64..0ea01ad 100644
--- a/day16/Makefile
+++ b/day16/Makefile
@@ -15,13 +15,13 @@ output:
 
 compile: ex1-c ex2-c
 
-ex1:
+ex1: ex1-c
 	@$(TIME) ex1.bash < $(INPUT) 2>&1
-	@$(TIME) ex1-c 2020 < $(INPUT) 2>&1
+	@$(TIME) ex1-c < $(INPUT) 2>&1
 
-ex2:
+ex2: ex2-c
 	@$(TIME) ex2.bash < $(INPUT) 2>&1
-	@#$(TIME) ex1-c 30000000 < $(INPUT) 2>&1
+	@$(TIME) ex2-c < $(INPUT) 2>&1
 
 clean:
 	@rm -f ex1-c ex2-c core
diff --git a/day16/ex1-c.c b/day16/ex1-c.c
index 74d93dc..e41880d 100644
--- a/day16/ex1-c.c
+++ b/day16/ex1-c.c
@@ -5,9 +5,6 @@
 #include <stdlib.h>
 #include <string.h>
 
-#define AA "ABCD"
-#define LAA sizeof(AA)
-
 /* tickets ranges */
 struct srange {
     char *name;
diff --git a/day16/ex1.bash b/day16/ex1.bash
index 31fc468..0b8f387 100755
--- a/day16/ex1.bash
+++ b/day16/ex1.bash
@@ -5,7 +5,7 @@
 CMD=${0##*/}
 #shopt -s extglob
 
-declare -A valid=()
+declare -A VALID=()
 declare -i state=0 res=0
 
 while read -r line; do
@@ -13,7 +13,7 @@ while read -r line; do
 		n1=$(seq "${BASH_REMATCH[2]}" "${BASH_REMATCH[3]}")
 		n2=$(seq "${BASH_REMATCH[5]}" "${BASH_REMATCH[6]}")
 		for i in $n1 $n2; do
-			valid[$i]=1
+			VALID[$i]=1
 		done
 	elif [[ $line =~ (your ticket:|nearby tickets) ]]; then
 		((state++))
@@ -21,7 +21,7 @@ while read -r line; do
 		if ((state == 2)); then
 			for i in ${line//,/ }; do
 				# shellcheck disable=SC2100
-				[[ ! -v valid[$i] ]] && res=res+i
+				[[ ! -v VALID[$i] ]] && res=res+i
 			done
 		fi
 	fi
diff --git a/day16/ex2-c.c b/day16/ex2-c.c
new file mode 100644
index 0000000..3ec0cc2
--- /dev/null
+++ b/day16/ex2-c.c
@@ -0,0 +1,243 @@
+/* ex1-c: Advent2020 game, day 16/game 1
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+/* tickets ranges */
+struct srange {
+    char *name;
+    int s1, e1;
+    int s2, e2;
+    int col;
+    int possiblecount;
+    int *possible;              /* possible[i]=-1 => column i cannot be */
+};
+
+struct list {
+    int size;
+    int last;
+    struct srange *ranges;
+} list = {
+    0, 0, NULL
+};
+
+#define BLOCKSIZE	1024    /* number of elements for realloc() */
+
+int *myticket=NULL;
+int *curticket=NULL;            /* current ticket */
+int ticketsize=0;
+
+void print_ranges()
+{
+    unsigned i, n=list.last;
+    int j;
+    struct srange *p=list.ranges;
+
+    printf("RANGES: address=%p last=%u size=%u\n", list.ranges, n, list.size);
+    for (i=0; i<n; ++i, ++p) {
+        printf("  [%03u] %u-%u %u-%u [%s]\n", i, p->s1, p->e1, p->s2, p->e2, p->name);
+        printf("    Possible cols (%d remaining) : ", p->possiblecount);
+        for (j=0; j<ticketsize; ++j)
+            if (p->possible[j] >= 0)
+                printf(" %d", p->possible[j]);
+        putchar('\n');
+    }
+}
+
+struct srange *add_range(name, s1, e1, s2, e2)
+    char *name;
+    int s1, e1, s2, e2;
+{
+    struct srange *p;
+
+    if (list.last == list.size) {
+        list.ranges=realloc(list.ranges, sizeof(struct srange)*BLOCKSIZE);
+        list.size+=BLOCKSIZE;
+    }
+    p=list.ranges+list.last;
+    p->name=strdup(name);
+    p->s1=s1;
+    p->e1=e1;
+    p->s2=s2;
+    p->e2=e2;
+    p->col=-1;
+    list.last++;
+    return p;
+}
+
+void print_ticket(ticket)
+    int *ticket;
+{
+    int i;
+    printf("Ticket: ");
+    for (i=0; i<ticketsize; ++i)
+        printf("%d ", *(ticket+i));
+    putchar('\n');
+}
+
+int *parse_ticket(str)
+    char *str;
+{
+    int i;
+    char *p;
+
+    if (!curticket)
+        curticket=malloc(ticketsize * sizeof *myticket);
+    for (i=0, p=str; i<ticketsize; ++i, ++p)
+        curticket[i]=(int)strtol(p, &p, 10);
+    return curticket;
+}
+
+int *parse_myticket(str)
+    char *str;
+{
+    int i, j, *possible;
+    char *p;
+
+    ticketsize=1;
+    for (p=str; *p; p++)
+        if (*p==',')
+            ticketsize++;
+
+    myticket=malloc(ticketsize * sizeof *myticket);
+    for (p=str, i=0; i<ticketsize; ++i, ++p)
+        myticket[i]=(int)strtol(p, &p, 10);
+    // set possible columns for all ranges
+    for (i=0; i<list.last; ++i) {
+        possible=malloc(sizeof (int) * ticketsize);
+        list.ranges[i].possible=possible;
+        list.ranges[i].possiblecount=ticketsize;
+        for (j=0; j<ticketsize; ++j)
+            possible[j]=j;
+    }
+    return myticket;
+}
+
+int is_in_range(i, range)
+    int i;
+    struct srange *range;
+{
+    if ((i>=range->s1 && i<=range->e1) || (i>=range->s2 && i<=range->e2))
+        return 1;
+    else
+        return 0;
+}
+
+int check_valid(ticket)
+    int *ticket;
+{
+    int i, r, found;
+
+    for (i=0; i<ticketsize; ++i) {
+        found=0;
+        for (r=0; r<list.last; ++r) {
+            if (is_in_range(*(ticket+i), list.ranges+r)) {
+                found=1;
+                break;
+            }
+        }
+        if (!found)
+            break;
+    }
+    return found;
+}
+
+void ex2_add(ticket)
+    int *ticket;
+{
+    int i, r;
+
+    if (check_valid(ticket)) {
+        for (i=0; i<ticketsize; ++i) {
+            for (r=0; r<list.last; ++r) {
+                if (!is_in_range(*(ticket+i), list.ranges+r)) {
+                    // this value cannot be in this range, we unset this column
+                    list.ranges[r].possible[i]=-1;
+                    list.ranges[r].possiblecount--;
+                }
+            }
+        }
+    }
+}
+
+unsigned long ex2()
+{
+    int i, r, r1, unique=0;
+    unsigned long res=1;
+    struct srange *range, *range1;
+
+    while (!unique) {
+        unique=1;
+        for (r=0; r<list.last; ++r) {
+            range=list.ranges+r;
+            if (range->col >= 0)
+                continue;
+            if (range->possiblecount == 1) {
+                for (i=0; range->possible[i]==-1 && i<ticketsize; ++i)
+                    ;
+                range->col=i;
+                for (r1=0; r1<list.last; ++r1) {
+                    range1=list.ranges+r1;
+                    if (range1 != range && range1->possible[i] != -1) {
+                        range1->possible[i]=-1;
+                        range1->possiblecount--;
+                        unique=0;
+                    }
+                }
+                break;
+            }
+        }
+    }
+    for (r=0; r<list.last; ++r) {
+        range=list.ranges+r;
+        if (!strncmp(range->name, "departure", 9)) {
+            res*=myticket[range->col];
+        }
+    }
+    return res;
+}
+
+int main(ac, av)
+    int ac;
+    char **av;
+{
+    char line[1024], pname[80], *elabel;
+    int s1, e1, s2, e2, end=0, status=0;
+    unsigned long res=0;
+    int *ticket;
+
+    while (fgets(line, sizeof line, stdin)) {
+        if (*line=='\n')
+            continue;
+        if (*line >= '0' && *line <= '9') {
+            switch (status) {
+                case 1:
+                    ticket=parse_myticket(line);
+                    // print_ranges();
+                    break;
+                case 2:
+                    ticket=parse_ticket(line);
+                    // valid ticket
+                    // print_ticket(ticket);
+                    ex2_add(ticket);
+                    break;
+            }
+            continue;
+        }
+        if (elabel=strchr(line, ':')) {
+            if (*(elabel+1)=='\n') {
+                status++;
+                continue;
+            }
+            sscanf(line, "%[^:]: %d-%d or %d-%d %n",
+                   pname, &s1, &e1, &s2, &e2, &end);
+            add_range(pname, s1, e1, s2, e2);
+
+        }
+    }
+    res=ex2();
+    printf("%s : res=%lu\n", *av, res);
+    exit (0);
+}