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`here I am writing a solution for concatenation of two arrays using but I come up with two solutions. the problems is given as below: Given an integer array nums of length n, you want to create an array ans of length 2n where ans[i] == nums[i] and ans[i + n] == nums[i] for 0 <= i < n (0-indexed).

Specifically, ans is the concatenation of two nums arrays.

Return the array ans. Example:

Input: nums = [1,2,1] Output: [1,2,1,1,2,1] Explanation: The array ans is formed as follows:

  • ans = [nums[0],nums[1],nums[2],nums[0],nums[1],nums[2]]
  • ans = [1,2,1,1,2,1]

Now,can anyone please explain me how can the space complexity of code (1) is better than that of the code (2)? Both solutions are made by me But I can't understand that how can be the time complexity of code (1) is better that of code (2). please explain this if you know how is code (1) better and taking less memory as compared to that of (2)? code (1) is taking memory of : 44.42 MB. code (2) is taking memory of : 44.72 MB. code(1) :

` class Solution { public int[] getConcatenation(int[] nums) {

 int n = nums.length;
 int[] arr = new int[2*n];
 int k = 0;
 int count = 0;
 for(int i = 0; i < n; i++){
     arr[k] = nums[i];
     k++;
     if(i == n-1){
         i = -1;
         count++;
     }
     if(count == 2){
         break;
     }
 }
 
return arr;

} }

 code (2) :
 class Solution {
 public int[] getConcatenation(int[] nums) {

 int n = nums.length;
 int[] arr = new int[2*n];

 
 for(int i = 0; i < 2*n; i++){
     arr[i] = nums[i % n];
 }

return arr; } }` Ask Question

Shantanu Patil
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    This is very hard to read because you did not use proper formatting. Look up markdown syntax and preview your posts in the SO question editor (where you wrote this question) to make a post that attract more readers. – Andreas Lundgren Jul 23 '23 at 20:41
  • For reference, the source of the problem seems to be https://leetcode.com/problems/concatenation-of-array/ – Old Dog Programmer Jul 23 '23 at 20:55
  • From an aesthetics point of view, I don't like the first solution in which the value of the `for` loop index is changed within the block controlled by the loop. Consider `for (m = 0; m < 2; m++) { for for(int i = 0; i < n; i++) { arr[k] = nums[i]; k++; } }` instead. – Old Dog Programmer Jul 23 '23 at 21:00
  • Off-topic: Can you think of a 3rd algorithm that will run in `for (int i = 0; i < n; i++) { }` ? Hint: There will be exactly 2 statements in the `{ }` block. – Old Dog Programmer Jul 23 '23 at 21:11
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    The space complexity seems to be the same in both cases. Where did you get those numbers from? – user207421 Jul 23 '23 at 23:34

1 Answers1

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Is 44.42/44.72 MB the memory used by the JVM during execution? Or is it the size in disc for the application?

In any case, the JVM is not "deterministic" in that sense, ghe GIT compiler can even change the memory used during the execution.

For Java memory management, there are tons of interesting metrics. But the one you are looking at is probably not one of them. I would suggest the following things to learn if you want to get starting understanding this field:

  • What is Stack vs. Heap.
  • Java memory management, Eden, Survivor, Tenured and other spaces.
  • Garbage collecfion.

With your code examples, investigate how they scale if you make your array 1 kb vs 1 mb long.

Andreas Lundgren
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