Shuffle the Array - Practice Coding Problems

Shuffle the Array - Problem

Array Easy

Given an 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].

Input & Output

Example 1 — Basic Case

$ Input: nums = [2,5,1,3,4,7], n = 3

› Output: [2,3,5,4,1,7]

💡 Note: First half is [2,5,1] and second half is [3,4,7]. Alternate: 2,3,5,4,1,7

Example 2 — Smaller Array

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

› Output: [1,4,2,3,3,2,4,1]

💡 Note: First half [1,2,3,4], second half [4,3,2,1]. Result: [1,4,2,3,3,2,4,1]

Example 3 — Minimum Size

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

› Output: [1,2,1,2]

💡 Note: First half [1,1], second half [2,2]. Alternate: [1,2,1,2]

Constraints

1 ≤ n ≤ 500
nums.length == 2n
1 ≤ nums[i] ≤ 10³

Visualization

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Understanding the Visualization

Input

Array of 2n elements: [x1,x2,...,xn,y1,y2,...,yn]

Process

Alternate picking from first half and second half

Output

Shuffled array: [x1,y1,x2,y2,...,xn,yn]

Key Takeaway

🎯 Key Insight: The shuffle creates an alternating pattern by interleaving elements from two equal halves

Asked in

a Amazon 15 🍎 Apple 12

The key insight is to recognize the alternating pattern between two halves of the array. The optimal approach uses direct index mapping where even positions take from the first half and odd positions take from the second half. Time: O(n), Space: O(n)

Common Approaches

Approach	Time	Space	Notes
✓ Two-Pass Array Construction	O(n)	O(n)	Create result array by alternating elements from first and second half
Direct Index Mapping	O(n)	O(n)	Calculate target position for each element directly using mathematical formula

Two-Pass Array Construction — Algorithm Steps

Step 1: Create empty result array
Step 2: Iterate from 0 to n-1
Step 3: Place nums[i] and nums[i+n] alternately

Visualization

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Step-by-Step Walkthrough

Split Conceptually

Identify first half [x1,x2,x3] and second half [y1,y2,y3]

Alternate Picking

Pick x1,y1 then x2,y2 then x3,y3

Result

Final shuffled array [x1,y1,x2,y2,x3,y3]

Code -

solution.c — C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void solution(int* nums, int numsSize, int n, int* result) {
    int index = 0;
    for (int i = 0; i < n; i++) {
        result[index++] = nums[i];
        result[index++] = nums[i + n];
    }
}

int main() {
    char line[1000];
    fgets(line, sizeof(line), stdin);
    
    // Parse array
    int nums[1000];
    int count = 0;
    char* token = strtok(line, "[],\n");
    while (token != NULL) {
        if (strlen(token) > 0) {
            nums[count++] = atoi(token);
        }
        token = strtok(NULL, "[],\n");
    }
    
    int n;
    scanf("%d", &n);
    
    int result[1000];
    solution(nums, count, n, result);
    
    printf("[");
    for (int i = 0; i < 2 * n; i++) {
        printf("%d", result[i]);
        if (i < 2 * n - 1) printf(",");
    }
    printf("]\n");
    
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(n)

Single pass through n elements

✓ Linear Growth

Space Complexity

O(n)

Result array stores n elements

⚡ Linearithmic Space

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Smart Actions

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Input & Output

Constraints

Visualization

Related Problems

Common Approaches

Two-Pass Array Construction — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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