sort and uniq combined using awk

Say, I have the following IP addresses file ip.txt :

cat > ip.txt
1.2.3.4
4.5.6.7
1.2.3.4
8.9.0.1
4.5.6.7

How to see the unique no. of ips in the above file ?

way 1: sort ip.txt | uniq

way 2 using awk : cat ip.txt | awk '!x[$0]++'