Exercise 4: Matching Pairs

Given a list of items, print all unique pairs (no repeats, no pairing with itself).

items = ["sword", "shield", "potion"]

Expected output:

sword + shield
sword + potion
shield + potion

Starter Code

items = ["sword", "shield", "potion"]

for i in range(len(items)):
    for j in range(___):
        print(f"{items[i]} + {items[j]}")

Hints

Hint 1 — Why not start j at 0?

If j starts at 0, you'd get repeated pairs like "shield + sword" after already printing "sword + shield". Starting j later avoids this.

Hint 2 — Where should j start?

Start the inner loop at i + 1. This means j is always after i, so you never repeat a pair or pair something with itself.

for j in range(i + 1, len(items)):

Hint 3 — Walk through it

When i = 0: j goes 1, 2 → sword+shield, sword+potion
When i = 1: j goes 2 → shield+potion
When i = 2: j has nothing left → done

3 items = 3 unique pairs!

Bonus Challenge

Try it with a longer list and count the total number of pairs:

items = ["sword", "shield", "potion", "bow", "staff"]
# How many unique pairs?

Solution

Show Solution

items = ["sword", "shield", "potion"]

for i in range(len(items)):
    for j in range(i + 1, len(items)):
        print(f"{items[i]} + {items[j]}")

Show Bonus Solution

items = ["sword", "shield", "potion", "bow", "staff"]
count = 0

for i in range(len(items)):
    for j in range(i + 1, len(items)):
        print(f"{items[i]} + {items[j]}")
        count += 1

print(f"\nTotal unique pairs: {count}")
# 5 items → 10 pairs

Matching Pairs

Exercise 4: Matching Pairs

Starter Code

Hints

Bonus Challenge

Solution

Try it yourself

Code: Matching Pairs