leetcode

Shuffle the Array - Link

Problem Description

Given the array nums consisting of 2n elements in the form [x1,x2,...,xn,y1,y2,...,yn].

Return the array in the form [x1,y1,x2,y2,...,xn,yn].

Examples

Example 1:

Input: nums = [2,5,1,3,4,7], n = 3
Output: [2,3,5,4,1,7] 
Explanation: Since x1=2, x2=5, x3=1, y1=3, y2=4, y3=7 then the answer is [2,3,5,4,1,7].

Example 2:

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

Example 3:

Input: nums = [1,1,2,2], n = 2
Output: [1,2,1,2]

Constraints

• 1 <= n <= 500
• nums.length == 2n
• 1 <= nums[i] <= 10^3

Solution

The approach is to iterate through the array and alternate between taking elements from the first half and second half:

1. Initialize two pointers: i starting at 0 (for first half) and j starting at n (for second half)
2. For each position m in the result array:
   • If m is even, take element from nums[i] and increment i
   • If m is odd, take element from nums[j] and increment j

This creates the interleaved pattern [x1,y1,x2,y2,...,xn,yn].

Implementation

class Solution {
    public int[] shuffle(int[] nums, int n) {
        int[] ans = new int[n * 2];
        int i = 0, j = n;
        for (int m = 0; m < n * 2; m++) {
            if (m % 2 == 0) {
                ans[m] = nums[i++];
            } else {
                ans[m] = nums[j++];
            }
        }
        return ans;
    }
}

Complexity Analysis

• Time Complexity: O(n) where n is the number of elements in each half
• Space Complexity: O(1) extra space (excluding the output array)
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