Second Largest Element - Problem

Given an array of integers, find the second largest element without sorting the array. The array may contain duplicates.

You need to handle edge cases where:

All elements are the same
Array has only two elements
Multiple elements have the same maximum value

Return the second largest distinct value. If no second largest element exists, return -1.

Input & Output

Example 1 — Basic Case

$ Input: nums = [3, 1, 4, 1, 5, 9, 2]

› Output: 5

💡 Note: The largest element is 9, and the second largest distinct element is 5

Example 2 — With Duplicates

$ Input: nums = [2, 2, 1, 3]

› Output: 2

💡 Note: The largest element is 3, and the second largest distinct element is 2

Example 3 — All Same Elements

$ Input: nums = [1, 1, 1, 1]

› Output: -1

💡 Note: All elements are the same, so no second largest distinct element exists

Constraints

2 ≤ nums.length ≤ 10⁴
-10⁹ ≤ nums[i] ≤ 10⁹

Visualization

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Asked in

a Amazon 45 G Google 38 M Microsoft 32 Apple 28

The key insight is to track only the two largest values in a single pass. The optimal approach maintains first and second variables, updating them as we scan through the array. Time: O(n), Space: O(1)

Common Approaches

✓ Single Pass with Two Variables

⏱️ Time: O(n) Space: O(1)

Maintain two variables for the largest and second largest values seen so far. Update them as we iterate through the array once, handling duplicates appropriately.

Sort and Find Second Largest

⏱️ Time: O(n log n) Space: O(1)

Sort the entire array in descending order, then iterate through to find the first element that's different from the maximum. This guarantees we find the second largest distinct value.

Single Pass with Two Variables — Algorithm Steps

Initialize first and second to minimum values
For each element, update first and second appropriately
Return second largest or -1 if not found

Visualization

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Step-by-Step Walkthrough

Initialize Variables

Set first and second to negative infinity

Process Each Element

Update first and second based on current value

Return Result

Second variable contains our answer

Code -

solution.c — C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>

int solution(int* nums, int size) {
    if (size < 2) {
        return -1;
    }
    
    long long first = LLONG_MIN;
    long long second = LLONG_MIN;
    
    for (int i = 0; i < size; i++) {
        if (nums[i] > first) {
            second = first;
            first = nums[i];
        } else if (nums[i] > second && nums[i] != first) {
            second = nums[i];
        }
    }
    
    return second == LLONG_MIN ? -1 : (int)second;
}

int main() {
    char line[10000];
    fgets(line, sizeof(line), stdin);
    
    // Parse JSON array manually
    int nums[1000];
    int size = 0;
    char* ptr = line + 1; // Skip [
    char* token;
    while ((token = strtok(ptr, ",]")) != NULL) {
        nums[size++] = atoi(token);
        ptr = NULL;
    }
    
    int result = solution(nums, size);
    printf("%d\n", result);
    
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(n)

Single pass through the array to find both largest values

⚡ Linearithmic

Space Complexity

O(1)

Only using two variables to track largest and second largest

✓ Linear Space

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Second Largest Element - Problem

Input & Output

Constraints

Visualization

Related Problems

Common Approaches

Single Pass with Two Variables — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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