Given a number N, the task is to find the number of pairs containing an even and an odd number from numbers between 1 and N inclusive.
Note:Order of numbers in the pair does not matter that is (1, 2) and (2, 1) are the same.
Input: N = 3 Output: 2 The pairs are (1, 2) and (2, 3). Input: N = 6 Output: 9 The pairs are (1, 2), (1, 4), (1, 6), (2, 3), (2, 5), (3, 4), (3, 6), (4, 5), (5, 6).
Approach: Number of ways to form the pairs is (Total number of Even numbers*Total number of Odd numbers).
- if N is even number of even numbers = number of odd numbers = N/2
- if N is odd number of even numbers = N/2 and number of odd numbers = N/2+1
Below is the implementation of the above approach:
Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.
- Count of integers in a range which have even number of odd digits and odd number of even digits
- Check if a number has an odd count of odd divisors and even count of even divisors
- Count numbers from given range having odd digits at odd places and even digits at even places
- Ways to choose balls such that at least one ball is chosen
- Find if it is possible to choose subarray that it contains exactly K even integers
- Count ways to make Bitwise XOR of odd and even indexed elements equal by removing an array element
- Count ways to make sum of odd and even indexed elements equal by removing an array element
- Count ways to express even number ‘n’ as sum of even integers
- Find a number containing N - 1 set bits at even positions from the right
- Count pairs in an array containing at least one even value
- Number of indices pair such that element pair sum from first Array is greater than second Array
- Number formed by deleting digits such that sum of the digits becomes even and the number odd
- Choose n elements such that their mean is maximum
- Choose points from two ranges such that no point lies in both the ranges
- Choose two elements from the given array such that their sum is not present in any of the arrays
- Puzzle | Choose the game of Rolling Dice
- Choose X such that (A xor X) + (B xor X) is minimized
- Pair formation such that maximum pair sum is minimized
- Sum of elements in range L-R where first half and second half is filled with odd and even numbers
- Generate an Array in which count of even and odd sum sub-arrays are E and O respectively
If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to email@example.com. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.