ReplaceElementsWithGreatestElementOnRightSide1299.kt

package easy

/*
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]
 */

fun replaceElements(arr: IntArray): IntArray {
    arr.forEachIndexed { i, _ ->
        arr[i] = arr.copyOfRange(i + 1, arr.size).getMaxElement()
    }
    return arr

}

fun IntArray.getMaxElement(): Int {
    if(this.isNotEmpty())
    {
        var max = this[0]
        for (i in 1 until this.size) {
            if (this[i] > max)
                max = this[i]
        }
        return max
    }
    return -1
}
/*
this solution enhance problem performance from O(N^2) to O(N)
Hint 1:
Loop through the array starting from the end.
Hint 2:
Keep the maximum value seen so far.
 */
fun replaceElementsSolution2(arr: IntArray): IntArray {
    var max=-1
    for ( i in arr.size-1 downTo 0)
    {
        val  temp=max
        if(arr[i]>max)
            max=arr[i]
        arr[i]=temp

    }
    return arr
}