Lists and Records

Min and Max Scan

Find the smallest and largest values in a list in a single pass. Seeding the running bounds from the first element avoids sentinel values; the trace shows exactly when each bound tightens.

By hand

Seed lo and hi from values[0] so no sentinel (0, float('inf')) is needed. Then scan the rest: lower the floor when a new minimum appears, raise the ceiling when a new maximum appears.

naive.py 
values = [5, 2, 8, 1, 9, 3, 7, 4]
lo = values[0]
hi = values[0]
for v in values[1:]:
    if v < lo:
        lo = v
    if v > hi:
        hi = v
print('RESULT:', (lo, hi))

The Pythonic way

The built-ins min and max each walk the list once internally in C. Two calls over eight values is negligible, and the intent is unambiguous.

library.py 
values = [5, 2, 8, 1, 9, 3, 7, 4]
lo = min(values)
hi = max(values)
print('RESULT:', (lo, hi))

RESULT: (1, 9)

Implementation notes

  • Seeding from values[0] is correct for any non-empty list of any comparable type; a sentinel like 0 or float('inf') would require assumptions about the data range.
  • In this run lo tightens twice (5→2→1) and hi rises twice (5→8→9); both progressions are visible in the trace.