Mastering Daily DSA Problems: A Step-by-Step Guide

Wrote a Java method to find the largest and second largest elements in an array. Handles edge cases like duplicates and single-element arrays.

Learned:

• Using Integer.MIN_VALUE for comparisons

• Avoiding duplicate values when finding second largest

• Simple O(n) pass through the array

1. Max and second max in an array

   /* Given an array arr[] of size N of positive integers which may have duplicates. * The task is to find the maximum and second maximum from the array, * and both of them should be different from each other, so If no second max exists, * then the second max will be -1. * Example 1: * Input: N = 3 arr[] = {2,1,2} * Output: 2 1 * Explanation: From the given array elements, 2 is the largest and 1 is the second largest. * Example 2: * Input: * N = 5 arr[] = {1,2,3,4,5} * Output: 5 4 * Explanation: From the given array elements, 5 is the largest and 4 is the second largest. */Check if array is sorted and rotated

    // Taking an array list result to return answer
            ArrayList<Integer> res = new ArrayList<>();
            // Assigning the smallest values to both large and second large 
            int largest = Integer.MIN_VALUE;
            int secondLargest = Integer.MIN_VALUE;
   
            // iteraring the whole array 
            for(int i = 0; i < n; i++ ){
                /* if array element is greater than our largest then 
                largest becomes second largest and the array element is assigned to largest */
                if (arr[i] > largest ) {
                    secondLargest = largest;            
                    largest = arr[i];              
                }
                /*if the current element is lesser than our largest and bigger than second largest  */
                else if (arr[i] != largest && arr[i] > secondLargest) {
                    secondLargest = arr[i];
                }
   
            }
            //add largest to array
            res.add(largest);
            // check if second large is not updated at all if not found assign -1
            if(secondLargest == Integer.MIN_VALUE){
                res.add(-1);
            }
            // if found add  secondlargest and return
            else{
                res.add(secondLargest);
            }
            return res;