LeetCode #3334 — MEDIUM

Find the Maximum Factor Score of Array

Move from brute-force thinking to an efficient approach using array strategy.

The Problem

Problem Statement

You are given an integer array nums.

The factor score of an array is defined as the product of the LCM and GCD of all elements of that array.

Return the maximum factor score of nums after removing at most one element from it.

Note that both the LCM and GCD of a single number are the number itself, and the factor score of an empty array is 0.

Example 1:

Input: nums = [2,4,8,16]

Output: 64

Explanation:

On removing 2, the GCD of the rest of the elements is 4 while the LCM is 16, which gives a maximum factor score of 4 * 16 = 64.

Example 2:

Input: nums = [1,2,3,4,5]

Output: 60

Explanation:

The maximum factor score of 60 can be obtained without removing any elements.

Example 3:

Input: nums = [3]

Output: 9

Constraints:

1 <= nums.length <= 100
1 <= nums[i] <= 30

Step 01

Brute Force Baseline

Problem summary: You are given an integer array nums. The factor score of an array is defined as the product of the LCM and GCD of all elements of that array. Return the maximum factor score of nums after removing at most one element from it. Note that both the LCM and GCD of a single number are the number itself, and the factor score of an empty array is 0.

Baseline thinking

Start with the most direct exhaustive search. That gives a correctness anchor before optimizing.

Pattern signal: Array · Math

Example 1

[2,4,8,16]

Example 2

[1,2,3,4,5]

Example 3

[3]

Core Insight

What unlocks the optimal approach

Use brute force approach with two loops.
Optimize using prefix and suffix arrays.

Interview move: turn each hint into an invariant you can check after every iteration/recursion step.

Step 03

Algorithm Walkthrough

Iteration Checklist

Define state (indices, window, stack, map, DP cell, or recursion frame).
Apply one transition step and update the invariant.
Record answer candidate when condition is met.
Continue until all input is consumed.

Use the first example testcase as your mental trace to verify each transition.

Step 04

Edge Cases

Minimum Input

Single element / shortest valid input

Validate boundary behavior before entering the main loop or recursion.

Duplicates & Repeats

Repeated values / repeated states

Decide whether duplicates should be merged, skipped, or counted explicitly.

Extreme Constraints

Upper-end input sizes

Re-check complexity target against constraints to avoid time-limit issues.

Invalid / Corner Shape

Empty collections, zeros, or disconnected structures

Handle special-case structure before the core algorithm path.

Step 05

Full Annotated Code

Source-backed implementations are provided below for direct study and interview prep.

// Accepted solution for LeetCode #3334: Find the Maximum Factor Score of Array
class Solution {
    public long maxScore(int[] nums) {
        int n = nums.length;
        long[] sufGcd = new long[n + 1];
        long[] sufLcm = new long[n + 1];
        sufLcm[n] = 1;
        for (int i = n - 1; i >= 0; --i) {
            sufGcd[i] = gcd(sufGcd[i + 1], nums[i]);
            sufLcm[i] = lcm(sufLcm[i + 1], nums[i]);
        }
        long ans = sufGcd[0] * sufLcm[0];
        long preGcd = 0, preLcm = 1;
        for (int i = 0; i < n; ++i) {
            ans = Math.max(ans, gcd(preGcd, sufGcd[i + 1]) * lcm(preLcm, sufLcm[i + 1]));
            preGcd = gcd(preGcd, nums[i]);
            preLcm = lcm(preLcm, nums[i]);
        }
        return ans;
    }

    private long gcd(long a, long b) {
        return b == 0 ? a : gcd(b, a % b);
    }

    private long lcm(long a, long b) {
        return a / gcd(a, b) * b;
    }
}

// Accepted solution for LeetCode #3334: Find the Maximum Factor Score of Array
func maxScore(nums []int) int64 {
	n := len(nums)
	sufGcd := make([]int64, n+1)
	sufLcm := make([]int64, n+1)
	sufLcm[n] = 1
	for i := n - 1; i >= 0; i-- {
		sufGcd[i] = gcd(sufGcd[i+1], int64(nums[i]))
		sufLcm[i] = lcm(sufLcm[i+1], int64(nums[i]))
	}

	ans := sufGcd[0] * sufLcm[0]
	preGcd, preLcm := int64(0), int64(1)
	for i := 0; i < n; i++ {
		ans = max(ans, gcd(preGcd, sufGcd[i+1])*lcm(preLcm, sufLcm[i+1]))
		preGcd = gcd(preGcd, int64(nums[i]))
		preLcm = lcm(preLcm, int64(nums[i]))
	}
	return ans
}

func gcd(a, b int64) int64 {
	if b == 0 {
		return a
	}
	return gcd(b, a%b)
}

func lcm(a, b int64) int64 {
	return a / gcd(a, b) * b
}

# Accepted solution for LeetCode #3334: Find the Maximum Factor Score of Array
class Solution:
    def maxScore(self, nums: List[int]) -> int:
        n = len(nums)
        suf_gcd = [0] * (n + 1)
        suf_lcm = [0] * n + [1]
        for i in range(n - 1, -1, -1):
            suf_gcd[i] = gcd(suf_gcd[i + 1], nums[i])
            suf_lcm[i] = lcm(suf_lcm[i + 1], nums[i])
        ans = suf_gcd[0] * suf_lcm[0]
        pre_gcd, pre_lcm = 0, 1
        for i, x in enumerate(nums):
            ans = max(ans, gcd(pre_gcd, suf_gcd[i + 1]) * lcm(pre_lcm, suf_lcm[i + 1]))
            pre_gcd = gcd(pre_gcd, x)
            pre_lcm = lcm(pre_lcm, x)
        return ans

// Accepted solution for LeetCode #3334: Find the Maximum Factor Score of Array
// Rust example auto-generated from java reference.
// Replace the signature and local types with the exact LeetCode harness for this problem.
impl Solution {
    pub fn rust_example() {
        // Port the logic from the reference block below.
    }
}

// Reference (java):
// // Accepted solution for LeetCode #3334: Find the Maximum Factor Score of Array
// class Solution {
//     public long maxScore(int[] nums) {
//         int n = nums.length;
//         long[] sufGcd = new long[n + 1];
//         long[] sufLcm = new long[n + 1];
//         sufLcm[n] = 1;
//         for (int i = n - 1; i >= 0; --i) {
//             sufGcd[i] = gcd(sufGcd[i + 1], nums[i]);
//             sufLcm[i] = lcm(sufLcm[i + 1], nums[i]);
//         }
//         long ans = sufGcd[0] * sufLcm[0];
//         long preGcd = 0, preLcm = 1;
//         for (int i = 0; i < n; ++i) {
//             ans = Math.max(ans, gcd(preGcd, sufGcd[i + 1]) * lcm(preLcm, sufLcm[i + 1]));
//             preGcd = gcd(preGcd, nums[i]);
//             preLcm = lcm(preLcm, nums[i]);
//         }
//         return ans;
//     }
// 
//     private long gcd(long a, long b) {
//         return b == 0 ? a : gcd(b, a % b);
//     }
// 
//     private long lcm(long a, long b) {
//         return a / gcd(a, b) * b;
//     }
// }

// Accepted solution for LeetCode #3334: Find the Maximum Factor Score of Array
function maxScore(nums: number[]): number {
    const n = nums.length;
    const sufGcd: number[] = Array(n + 1).fill(0);
    const sufLcm: number[] = Array(n + 1).fill(1);
    for (let i = n - 1; i >= 0; i--) {
        sufGcd[i] = gcd(sufGcd[i + 1], nums[i]);
        sufLcm[i] = lcm(sufLcm[i + 1], nums[i]);
    }

    let ans = sufGcd[0] * sufLcm[0];
    let preGcd = 0,
        preLcm = 1;
    for (let i = 0; i < n; i++) {
        ans = Math.max(ans, gcd(preGcd, sufGcd[i + 1]) * lcm(preLcm, sufLcm[i + 1]));
        preGcd = gcd(preGcd, nums[i]);
        preLcm = lcm(preLcm, nums[i]);
    }
    return ans;
}

function gcd(a: number, b: number): number {
    return b === 0 ? a : gcd(b, a % b);
}

function lcm(a: number, b: number): number {
    return (a / gcd(a, b)) * b;
}

Step 06

Interactive Study Demo

Use this to step through a reusable interview workflow for this problem.

Custom checkpoints (one per line)

Press Step or Run All to begin.

Step 07

Complexity Analysis

Time

O(n)

Space

O(1)

Approach Breakdown

BRUTE FORCE

O(n²) time

O(1) space

Two nested loops check every pair or subarray. The outer loop fixes a starting point, the inner loop extends or searches. For n elements this gives up to n²/2 operations. No extra space, but the quadratic time is prohibitive for large inputs.

OPTIMIZED

O(n) time

O(1) space

Most array problems have an O(n²) brute force (nested loops) and an O(n) optimal (single pass with clever state tracking). The key is identifying what information to maintain as you scan: a running max, a prefix sum, a hash map of seen values, or two pointers.

Shortcut: If you are using nested loops on an array, there is almost always an O(n) solution. Look for the right auxiliary state.

Coach Notes

Common Mistakes

Review these before coding to avoid predictable interview regressions.

Off-by-one on range boundaries

Wrong move: Loop endpoints miss first/last candidate.

Usually fails on: Fails on minimal arrays and exact-boundary answers.

Fix: Re-derive loops from inclusive/exclusive ranges before coding.

Overflow in intermediate arithmetic

Wrong move: Temporary multiplications exceed integer bounds.

Usually fails on: Large inputs wrap around unexpectedly.

Fix: Use wider types, modular arithmetic, or rearranged operations.