List में दूसरा सबसे बड़ा Number — code और dry run

Problem statement

Approach 1: simple loop

Remove the maximum, then take the maximum of what remains — the two-step version that reads exactly like the problem statement.

nums = [12, 45, 2, 41]

copy = nums[:]          # keep the original untouched
copy.remove(max(copy))  # drop ONE occurrence of the largest

print(max(copy))
# Output: 41

remove() deletes only the first matching occurrence, so duplicates of the maximum survive — which is what the "duplicates count" reading wants. Work on a copy so the original list is intact for later use.

Approach 2: reusable function

For the distinct reading, collapse duplicates with a set first, sort, and pick the second from the end — the version most exams and interviews mean.

nums = [12, 45, 45, 2]

unique = sorted(set(nums))
print(unique[-2])
# Output: 12

Build it defensively and the edge cases say their names: a list with fewer than two distinct values has no second largest at all.

def second_largest(nums):
    unique = sorted(set(nums))
    if len(unique) < 2:
        return None          # explicitly: there is no answer
    return unique[-2]

Approach 3: Pythonic alternative

One pass, two variables: walk the list once, tracking the largest and second largest seen so far. This is the version that scales — it also works streaming over data you cannot sort.

nums = [12, 45, 2, 41]

first = second = float("-inf")
for n in nums:
    if n > first:
        second = first     # old champion demoted
        first = n
    elif first > n > second:
        second = n

print(second)
# Output: 41

Starting both at negative infinity means any real number beats them — even a list of all-negative numbers works. Note the chained comparison first > n > second, which skips duplicates of the champion.

Dry run

Common errors

• Original list को ही sort कर देना — copy बनाकर या sorted() से करो।
• Duplicates पर [-2] उठा लेना — पहले तय करो कि duplicates गिनने हैं या distinct।
• Second को 0 से शुरू करना — सब negative list पर गलत; float("-inf") लो।
• छोटी list का case — [7] या [7, 7] में दूसरा distinct है ही नहीं; None return करो।
• Purana champion खो देना — second = first पहले, first = n बाद में।

Practice on PyDebug

Concept समझने के बाद इन free problems को browser में solve करें:

• Range boundary practice
• Operator precedence practice
• Variables and assignment practice