Warm Up · Second Largest

Find the Second Largest Number in an Array

Problem Statement

Write a function secondLargest(arr) that returns the second largest distinct number in an array.

The array must contain at least two elements.
If all elements are equal, return: No second largest found.
If the array has fewer than two elements, return: Array should have at least two numbers.

Input: arr = [0, 3, 5, 2, 7, 9]→Output: 7

Input: arr = [4, 4, 4, 4]→Output: No second largest found

Input: arr = [5]→Output: Array should have at least two numbers

Input: arr = [10, 20]→Output: 10

Check the array length. If there are fewer than 2 elements, return the appropriate message.
Use two variables: firstLargest and secondLargest.
Ignore duplicates by checking num !== firstLargest before assigning secondLargest.

Time Complexity: O(n) - single pass through the array.

Space Complexity: O(1) - constant space.

1Start with the array[0, 3, 5, 5, 2, 7, 9]

2Track the first largestfirst = 9

3Duplicate values are ignorede.g. 5

4Second largest7

When a new maximum appears, the old first slides down into second before first is updated.
A value between second and first only replaces second if it is not equal to first.
If second is still -Infinity at the end, every element was the same.

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