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Find the Second Largest Number in a List

Certification: Basic Level Accuracy: 45.12% Submissions: 82 Points: 10

Write a Python program that finds the second largest number in a given list of integers. If all elements are equal or there are fewer than 2 elements, return -1.

Example 1
    

  • Input: nums = [10, 5, 7, 15, 20]
    • 

  • Output: 15
    • 

  • Explanation: 

      

    • Step 1: Find the largest number in the list: 20.
      • 

    • Step 2: Find the largest number that is not equal to the largest: 15.
      • 

    • Step 3: Return 15 as the second largest number.
      • 

    

    •
Example 2
    

  • Input: nums = [3, 3, 3, 3]
    • 

  • Output: -1
    • 

  • Explanation: 

      

    • Step 1: Find the largest number in the list: 3.
      • 

    • Step 2: Try to find a number less than 3, but all elements are equal.
      • 

    • Step 3: Since all elements are equal, return -1.
      • 

    

    •
Constraints
    

  • 0 ≤ len(list) ≤ 10^6
    • 

  • List elements are integers
    • 

  • Time Complexity: O(n)
    • 

  • Space Complexity: O(1)
    •
NumberListTech MahindraSnowflake
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Hint
Solution

Solution Hints

    
  
  • Sort the list and return the second last element if there are at least two unique numbers
    • 
  
  • Track both maximum and second maximum while iterating through the list
    • 
  
  • Handle edge cases like empty lists, lists with one element, or lists with all identical elements
    •

Steps to solve by this approach:

 Step 1: Check if the list has at least 2 elements, return -1 if not.

 Step 2: Initialize two variables to track the largest and second largest values.

 Step 3: Iterate through each number in the input list.

 Step 4: If current number is larger than the largest, update both largest and second largest.

 Step 5: If current number is between largest and second largest, update only second largest.

 Step 6: Check if a valid second largest was found (not still the initial value).

 Step 7: Return the second largest number or -1 if all elements are equal.

Submitted Code :