Super Egg Drop

Updated on 26 June, 2025
Super Egg Drop header image

Problem Statement

In this problem, you are equipped with k identical eggs and a building of n floors labeled from 1 through n. There is a specific floor labeled f within the range from 0 to n where the behavior of an egg when dropped changes distinctly. If an egg is dropped from any floor above the fth floor, it will break. Conversely, dropping an egg from the fth floor or any floor below it will not cause the egg to break. The challenge, using the eggs, is to determine the exact floor f with certainty.

Each attempt to identify this floor involves selecting a floor x, where 1 <= x <= n, and dropping an egg. Depending on whether the egg breaks or remains intact, you either discard or reuse the egg for another test. The objective is to find the minimal number of such attempts needed to conclusively identify the value of floor f.

Examples

Example 1

Input:

k = 1, n = 2

Output:

2

Explanation:

Drop the egg from floor 1. If it breaks, we know that f = 0.
Otherwise, drop the egg from floor 2. If it breaks, we know that f = 1.
If it does not break, then we know f = 2.
Hence, we need at minimum 2 moves to determine with certainty what the value of f is.

Example 2

Input:

k = 2, n = 6

Output:

3

Example 3

Input:

k = 3, n = 14

Output:

4

Constraints

  • 1 <= k <= 100
  • 1 <= n <= 104

Approach and Intuition

The task entails an optimization process aimed at determining the threshold floor (f) using the fewest trials, given a certain number of eggs. Here's a guided approach based on the examples provided:

  1. Understanding the constraints and iterative reduction:

    • For k = 1 (one egg): The strategy shifts to a simple linear search — drop from floor 1 up to n, breaking the sequence once the egg breaks.
    • More than one egg introduces the potential to use more complex strategies involving dividing the building into sections and minimizing the worst-case number of drops needed.
  2. Utilizing Binary Search with a Backup:

    • If you possess several eggs, starting from a middle floor enables a binary search-like approach. Upon a break, one can turn to lower floors; if it doesn't, you move higher. The extra eggs serve as backups decreasing risk and refining accuracy with each subsequent trial.
  3. Balanced Approach in Higher k scenarios:

    • When k is greater than 1 and n is large, a balanced approach — not too linear and not as risky as halving each time — could be essential. Reducing potential attempts both in the scenarios where the egg breaks early and where it does not is key.
  4. Dynamic Programming Optimization:

    • For larger values of k and n, employing a dynamic programming technique can help calculate the minimum drops required in a bottom-up manner. This means progressively building the solution starting from the smallest sub-problems (e.g., lowest floors, fewest eggs) up to the main problem size defined by k and n.
  5. Edge Cases Handling:

    • Always test edge scenarios such as n=1 (only one floor) or very high n with smaller k. These edge cases could potentially highlight flaws in the approach which assumes too many resources or computational steps.

By integrating these approaches, you can refine your strategy to determine the critical floor f using minimal moves, considering both the constraints of egg availability and the floor height of the building.

Solutions

  • Java
  • Python
java
class Solution {
    public int calculateDrops(int eggs, int floors) {
        int low = 1, high = floors;
        while (low < high) {
            int mid = (low + high) / 2;
            if (eggDropHelper(mid, eggs, floors) < floors)
                low = mid + 1;
            else
                high = mid;
        }

        return low;
    }

    public int eggDropHelper(int currentFloor, int eggs, int floors) {
        int sum = 0, combination = 1;
        for (int i = 1; i <= eggs; ++i) {
            combination *= currentFloor - i + 1;
            combination /= i;
            sum += combination;
            if (sum >= floors) break;
        }
        return sum;
    }
}

The provided Java solution implements an algorithm to determine the minimum number of attempts needed to find out from which floor eggs can be dropped without breaking, given a certain number of eggs and floors. This is known as the "Super Egg Drop" problem, a typical example of a dynamic programming and binary search combination challenge.

The code consists of two main functions:

  • calculateDrops(int eggs, int floors) - This method applies a binary search mechanism to minimize the number of drops required to find the critical floor. It initializes low to 1 and high to the number of floors, then iteratively narrows down the range by setting a middle floor (mid). It uses the helper method eggDropHelper to determine if the current middle floor can serve as the breaking point for egg drops with fewer attempts. If the helper method returns a value less than the number of floors, it shifts the low boundary up, otherwise it adjusts the high boundary.

  • eggDropHelper(int currentFloor, int eggs, int floors) - Employed within the binary search, this helper function computes the sum of combinations which represent possible scenarios of dropping eggs from a certain floor. By iterating through the number of eggs and using a formula for combinations (applying the binomial coefficient), it cumulatively checks if the current sum of combinations is sufficient to cover all floors. If it reaches or surpasses the number of floors, it breaks out of the loop.

The overall approach efficiently reduces the number of checks (i.e., egg drops) needed to find the minimum number of trials required in the worst-case scenario by using a binary search alongside dynamic programming principles to manage complexity. This solution tailors the calculation of attempts dynamically based on changing mid points evaluated by the binary search process, adjusting combinations with regard to both the current floor and available eggs to determine the minimum required drops effectively.

python
class Solution:
    def eggDrop(self, eggs: int, floors: int) -> int:
        def calc_moves(move):
            total_moves = 0
            increment = 1
            for level in range(1, eggs + 1):
                increment *= move - level + 1
                increment //= level
                total_moves += increment
                if total_moves >= floors: break
            return total_moves

        low, high = 1, floors
        while low < high:
            mid = (low + high) // 2
            if calc_moves(mid) < floors:
                low = mid + 1
            else:
                high = mid
        return low

The Python script provided efficiently solves the "Super Egg Drop" problem by determining the minimum number of attempts needed to figure out from which floor eggs will break, using a given number of eggs and floors. Here’s a breakdown of how the solution works:

  • The function eggDrop receives the number of eggs and floors as parameters and utilizes a helper nested function calc_moves.
  • calc_moves calculates whether a specific number of moves is sufficient to test all the floors with the given eggs. It uses a mathematical approach to sum possible combinations (ways to distribute the moves among the floors) and determines if they cover the range of floors from 1 to the specified number.
  • The main function then applies binary search to minimize the number of required moves. low represents the minimum number of moves (starting at 1), and high is initialized to the number of floors.
  • During each iteration of the loop, it computes the midpoint (mid) and checks using calc_moves whether mid moves suffice:
    • If mid moves are not enough, it increases low to mid + 1.
    • If they are sufficient, it sets high to mid.
  • The algorithm continues until low meets high, at which point low gives the minimum number of moves needed to ensure the eggs won’t needlessly break.

This approach is efficient because it reduces the problem size logarithmically with the binary search and avoids exhaustive checking of every scenario by using mathematical optimization from combinations theory.

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