Second Largest Element in Java: Solution, Explanation & Practice

Find the second largest element

Problem summary

Write a program that finds the second largest element in an array.

Starter code

public class Main {
    public static void main(String[] args) {
        int[] arr = {12, 35, 1, 10, 34, 1}; // Test case 1
        
        // Find second largest
        // Print: Second largest: <result>
    }
}

Expected output and test cases

Second largest in array
```
Second largest: 34
```
From [1,2,3,4,5]
```
Second largest: 4
```
From [9,9,9,9]
```
Second largest: 9
```

Hints

Track both largest and second largest
Update both as you iterate
Handle duplicates carefully

Validated solution

Reveal Java solution

public class Main {
    static int secondLargestDistinct(int[] values) {
        Integer largest = null;
        Integer second = null;
        for (int value : values) {
            if (largest == null || value > largest) {
                second = largest;
                largest = value;
            } else if (value != largest && (second == null || value > second)) {
                second = value;
            }
        }
        if (second == null) throw new IllegalArgumentException("need two distinct values");
        return second;
    }

    public static void main(String[] args) {
        System.out.println("Second largest: " + secondLargestDistinct(new int[] {12, 45, 9, 34, 18}));
    }
}

How to approach the problem

Track the largest and second-largest distinct values in one pass. A new largest pushes the old largest into second place; a duplicate of the largest must not become the answer.

Approach

Represent missing candidates explicitly.
Promote the old largest when a new largest arrives.
Update second only for a distinct in-between value.

Time and space complexity

Time: O(n). Space: O(1).

Edge cases to test

All-equal arrays have no second distinct value.
Negative values work because no numeric sentinel is used.

Common mistakes

Sorting only to find two values when input order need not change.
Treating a duplicate maximum as second largest.

Follow-up challenge

Return the k-th distinct largest value using a bounded min-heap.

Related Arrays exercises

Practice all Arrays exercises · Run this idea in the Java compiler