LeetCode Challenge: 238. Product of Array Except Self - JavaScript Solution 🚀

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This problem challenges you to compute a product array without directly using division, making it a test of algorithmic efficiency and logical thinking. Let's break down LeetCode 238: Product of Array Except Self and implement a solution in O(n) time.

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🚀 Problem Description

Given an integer array nums, return an array answer where:

• answer[i] is the product of all elements in nums except nums[i].
• You must solve it without division and in O(n) time.

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💡 Examples
Example 1

Input: nums = [1,2,3,4]  
Output: [24,12,8,6]  
Explanation:  
- `answer[0] = 2 * 3 * 4 = 24`  
- `answer[1] = 1 * 3 * 4 = 12`  
- `answer[2] = 1 * 2 * 4 = 8`  
- `answer[3] = 1 * 2 * 3 = 6`

Example 2

Input: nums = [-1,1,0,-3,3]  
Output: [0,0,9,0,0]  
Explanation:  
- `answer[2] = -1 * 1 * -3 * 3 = 9`  
- For all other indices, the product includes `0`.

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🏆 JavaScript Solution

The solution involves using two prefix and suffix arrays to calculate the product of all elements except the current index without division.

var productExceptSelf = function(nums) {
    let n = nums.length;
    let answer = new Array(n).fill(1);

    let prefix = 1;
    for (let i = 0; i < n; i++) {
        answer[i] = prefix;
        prefix *= nums[i];
    }

    let suffix = 1;
    for (let i = n - 1; i >= 0; i--) {
        answer[i] *= suffix;
        suffix *= nums[i];
    }

    return answer;
};

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🔍 How It Works

1. Prefix Product Pass:

   • Compute the cumulative product of elements to the left of each index and store it in the answer array.

2. Suffix Product Pass:

   • Traverse the array from right to left and multiply the cumulative product of elements to the right of each index with the value in answer.

3. The result is an array where each element is the product of all other elements except itself.

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🔑 Complexity Analysis

• > Time Complexity: O(n), since we traverse the array twice (once for prefix and once for suffix).
• > Space Complexity: O(1) (ignoring the output array), as we do not use any additional data structures apart from the result array.

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📋 Dry Run

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

Output: [24, 12, 8, 6]

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✨ Pro Tips for Interviews

1. Clarify requirements: Confirm whether division is allowed (it’s not in this problem).
2. Handle edge cases:
   • Single-element array ([a] → [1]).
   • Arrays with zeros ([0,1,2] → [2,0,0]).
3. Optimize space: Explain how avoiding auxiliary arrays reduces space complexity.

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📚 Learn More

Check out the full explanation and code walkthrough on my Dev.to post:
👉 Insert Delete GetRandom O(1) - JavaScript Solution

How would you solve this problem? Let’s discuss below! 🚀

JavaScript #LeetCode #CodingInterview #ProblemSolving

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[Rahul Kumar Barnwal]

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