Python Tools for DSA

This is the Python toolkit that shows up again and again in DSA solutions.

Lists

nums = [10, 20, 30]
nums.append(40)
last = nums.pop()

print(nums)
print(last)
print(nums[0], nums[-1])

Dictionaries

counts = {}
for ch in "banana":
    counts[ch] = counts.get(ch, 0) + 1

print(counts)

Sets

seen = set()

for x in [3, 1, 4, 1, 5]:
    if x in seen:
        print("duplicate:", x)
        break
    seen.add(x)

Tuples

Tuples are useful when you want an immutable pair like (row, col) or (distance, node).

point = (2, 5)
row, col = point
print(row, col)

Useful built-ins

nums = [7, 2, 9, 4]

print("sorted:", sorted(nums))
print("min:", min(nums))
print("max:", max(nums))
print("sum:", sum(nums))

Interview habit

Before writing a custom data structure in Python, ask:

• Can list solve this?
• Do I need a set for membership?
• Do I need a dict for lookup?
• Is a tuple the cleanest key or state representation?