Complete Array-1

[PrakarshKamal]

No description provided.

[super30admin]

Evaluation completed, but no feedback text was generated.

[super30admin]

Dear student,

Thank you for your submission. I see that you have attempted the "Product Except Self" problem and also provided solutions for other problems. However, I will focus on the "Product Except Self" solution.

Strengths:

• You have attempted to optimize the solution to O(n) time and O(1) space, which is the follow-up requirement.
• You have used meaningful variable names like runningProduct and ans.

Areas for Improvement:

1. Correctness: Your current implementation for productExceptSelf has several errors. Specifically:

   • In the first loop, you start at i=0 and then access nums[i-1], which causes an index out of bounds exception. You should start the loop from i=1 instead of i=0.
   • The logic for the prefix product is incorrect. The prefix product for index i should be the product of all elements from index 0 to i-1. Your loop should be:

     for (int i = 1; i < n; i++) {
         ans[i] = ans[i-1] * nums[i-1];
     }
     

   • In the second loop, you are trying to compute the postfix product and multiply it with the prefix product stored in ans. However, your code uses runningProduct = runningProduct * ans[i+1] which is not correct. Instead, you should maintain a running product for the postfix and multiply it with the existing value in ans[i]. The correct approach is:

     int postfix = 1;
     for (int i = n-1; i >= 0; i--) {
         ans[i] = ans[i] * postfix;
         postfix = postfix * nums[i];
     }
     

   • Also, note that in the second loop, you should iterate from n-1 down to 0, not from n-2.

2. Code Quality: Please ensure that you test your code with sample inputs to avoid syntax and logical errors. Also, comment out unused code properly to avoid confusion.

3. Relevance: The problem requires a solution for "Product Except Self", but you have included solutions for other problems (like diagonal traversal and spiral traversal). While it's good to practice, make sure to submit only the relevant code for the problem at hand.

Here is a corrected version of your solution for "Product Except Self":

class Solution {
    public int[] productExceptSelf(int[] nums) {
        int n = nums.length;
        int[] ans = new int[n];
        
        // Initialize the first element of ans to 1
        ans[0] = 1;
        
        // Compute prefix products
        for (int i = 1; i < n; i++) {
            ans[i] = ans[i-1] * nums[i-1];
        }
        
        int postfix = 1;
        // Multiply with postfix products
        for (int i = n-1; i >= 0; i--) {
            ans[i] = ans[i] * postfix;
            postfix = postfix * nums[i];
        }
        
        return ans;
    }
}

I encourage you to understand this corrected version and practice more to avoid such errors in the future.