No_1299.cs

/*
Given an array arr, replace every element in that array with the greatest element among the elements to its right, and replace the last element with -1.

After doing so, return the array.

 

Example 1:

Input: arr = [17,18,5,4,6,1]
Output: [18,6,6,6,1,-1]
Explanation: 
- index 0 --> the greatest element to the right of index 0 is index 1 (18).
- index 1 --> the greatest element to the right of index 1 is index 4 (6).
- index 2 --> the greatest element to the right of index 2 is index 4 (6).
- index 3 --> the greatest element to the right of index 3 is index 4 (6).
- index 4 --> the greatest element to the right of index 4 is index 5 (1).
- index 5 --> there are no elements to the right of index 5, so we put -1.
Example 2:

Input: arr = [400]
Output: [-1]
Explanation: There are no elements to the right of index 0.
 

Constraints:

1 <= arr.length <= 104
1 <= arr[i] <= 105
*/
namespace LeetCode
{
    public class No_1299{
        public int[] ReplaceElements(int[] arr)
        {
            for (int i = 0; i < arr.Length - 1; i++)
            {
                int pmax = i + 1, max = arr[i + 1], p = i + 2;
                while (p < arr.Length)
                {
                    if (max < arr[p])
                    {
                        pmax = p;
                        max = arr[p];
                    }
                    p++;
                }

                for (int j = i; j < pmax; j++)
                {
                    arr[j] = max;
                }
                i = pmax - 1;
            }

            arr[arr.Length - 1] = -1;
            return arr;
        }
    }
}