Python Program for Interlace odd / even from A to B

Print odd numbers from A to B interlaced with even numbers from B to A

Understand the Problem

Problem Statement

Two numbers A and B are passed as input. The program must print the odd numbers from A to B (inclusive of A and B) interlaced with the even numbers from B to A.

Constraints

1 <= A <= 9999999
A < B <= 9999999
Input values are positive integers
Output must be space-separated numbers

Examples

Example 1

Input

5
11

Output

5 10 7 8 9 6 11

Explanation

Odd numbers from 5 to 11: 5, 7, 9, 11. Even numbers from 11 to 5: 10, 8, 6. Since odd count (4) > even count (3), start with odd: 5 → 10 → 7 → 8 → 9 → 6 → 11.

Example 2

Input

4
14

Output

14 5 12 7 10 9 8 11 6 13 4

Explanation

Odd numbers from 4 to 14: 5, 7, 9, 11, 13 (count=5). Even numbers from 14 to 4: 14, 12, 10, 8, 6, 4 (count=6). Since even count > odd count, start with even: 14 → 5 → 12 → 7 → 10 → 9 → 8 → 11 → 6 → 13 → 4.

Example 3

Input

3
12

Output

3 12 5 10 7 8 9 6 11 4

Explanation

Odd numbers from 3 to 12: 3, 5, 7, 9, 11 (count=5). Even numbers from 12 to 3: 12, 10, 8, 6, 4 (count=5). Since counts are equal, start with odd: 3 → 12 → 5 → 10 → 7 → 8 → 9 → 6 → 11 → 4.

Solution

#include <stdio.h>

int main() {
    int a, b;
    scanf("%d", &a);
    scanf("%d", &b);
    
    int odd[10000000], even[10000000];
    int odd_count = 0, even_count = 0;
    
    // Generate odd numbers from A to B
    for (int i = a; i <= b; i++) {
        if (i % 2 != 0) {
            odd[odd_count++] = i;
        }
    }
    
    // Generate even numbers from B to A
    for (int i = b; i >= a; i--) {
        if (i % 2 == 0) {
            even[even_count++] = i;
        }
    }
    
    int i = 0, j = 0;
    int start_with_even = (even_count > odd_count) ? 1 : 0;
    
    // Interlace the numbers
    while (i < odd_count || j < even_count) {
        if (start_with_even) {
            if (j < even_count) {
                printf("%d ", even[j++]);
            }
            if (i < odd_count) {
                printf("%d ", odd[i++]);
            }
        } else {
            if (i < odd_count) {
                printf("%d ", odd[i++]);
            }
            if (j < even_count) {
                printf("%d ", even[j++]);
            }
        }
    }
    
    return 0;
}

Time:O(B-A)

Space:O(B-A)

Approach:

C Solution Explanation:

Read input values A and B using scanf
Create arrays to store odd and even numbers
First loop: iterate from A to B, collect odd numbers into odd[] array
Second loop: iterate from B to A, collect even numbers into even[] array
Count the number of odd and even numbers
Determine which sequence to start with: if even_count > odd_count, start with even numbers
Use a while loop to interlace the numbers, alternating between the two arrays
Print each number followed by a space

The solution uses arrays to store the numbers and simple index manipulation to interlace them.

Visual Explanation

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