Replace Elements with Greatest Element on Right Side

Problem Description

Ah, the classic “Replace Elements with Greatest Element on Right Side” problem! It’s like that moment when you realize your friend has a better phone than you, and you just want to replace your old model with theirs. The task is simple: for each element in an array, replace it with the greatest element to its right. If there’s no element to the right, replace it with -1.

Imagine you’re at a party, and you’re the last one to know that the best dance moves are happening right behind you. You’d want to turn around and learn those moves, right? Well, this problem is all about turning around and seeing what’s better behind you!

Code Solution


class Solution:
    def replaceElements(self, arr: list[int]) -> list[int]:
        maxOfRight = -1
        for i in reversed(range(len(arr))):
            arr[i], maxOfRight = maxOfRight, max(maxOfRight, arr[i])
        return arr

Approach

The approach taken in the provided code is straightforward yet efficient. We traverse the array from the end to the beginning, keeping track of the maximum value encountered so far. For each element, we replace it with this maximum value, and then update the maximum for the next iteration. This way, we ensure that each element gets replaced with the greatest element to its right without needing nested loops.

Time and Space Complexity

Complexity Type	Complexity
Time Complexity	O(n)
Space Complexity	O(1)

Real-World Example

Let’s say you’re at a buffet, and you’re eyeing that last slice of cake. You look around and see everyone else has already taken their favorite desserts. You want to know what’s the best dessert left before you make your choice. This problem is akin to that scenario—replacing your choice with the best option available to you at that moment!