This was fun - missing.c:
void die(int err, char *msg) {
err? fprintf(stderr, "%s\n", msg), exit(1): 0;
}
int main(int argc, char *argv[]) {
int n, answer = 1, val;
die(argc != 2 || (n = atoi(argv[1])) < 2, "Usage: missing n");
for (; n > 1; n--) {
die(scanf("%d", &val) != 1, "Error reading input");
answer ^= val ^ n;
}
printf("%d\n", answer);
}
Test with:
seq 1 100 | shuf > /tmp/missing.dat
cc -o missing missing.c
&& for i in $(seq 1 100); do
if [[ $(sed -n ${i}p /tmp/missing.dat) != $(sed ${i}d /tmp/missing.dat | ./missing 100) ]]; then
echo -n "[$i wrong]"
else
echo -n .
fi
done
echo
And yes, I'm insecurely using atoi and scanf. The alternatives used too many characters for a mastodon post.
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