1679 Max Number of K-Sum Pairs 1

Joel Castillo Espinosa 2

DESCRIPTION

You are given an integer array nums and an integer k.

In one operation, you can pick two numbers from the array whose sum equals k and remove them from the array.

Return the maximum number of operations you can perform on the array.

Examples

  • Example 1:
    • Input: nums = [1,2,3,4], k = 5
    • Output: 2
    • Explanation: Starting with nums = [1,2,3,4]:
      • Remove numbers 1 and 4, then nums = [2,3]
      • Remove numbers 2 and 3, then nums = [] There are no more pairs that sum up to 5, hence a total of 2 operations.
  • Example 2:
    • Input: nums = [3,1,3,4,3], k = 6
    • Output: 1
    • Explanation: Starting with nums = [3,1,3,4,3]:
      • Remove the first two 3’s, then nums = [1,4,3] There are no more pairs that sum up to 6, hence a total of 1 operation.

Constraints:

  • 1 ≤ nums.length ≤ $10^{5}$

  • 1 ≤ nums[i] ≤ $10^{9}$

  • 1 ≤ k ≤ $10^{9}$

SOLUTION 3

ksum_pairs <- function(nums, k){
  nums1 <- nums
  count <- 0 # start the number of operations
  
  # in each iteration take the i-element and 
    # evaluate if satisfy the sum with other number in nums
  while (length(nums1) > 1) { # it is need at least 2 elements
    # check if i-element with other sum to k (in vector check)
    dif <- k - nums1[1] 
    nums1 <- nums1[-1] # drop the i-element
    check <- nums1 == dif 
    
    if(sum(check) > 0){ # if at least one element satisfies sum
      id <- c(1:length(check))
      # drop just the first element that satisfies the sum
       # others could be used in next iterations
      nums1 <- nums1[-id[check][1]]
      count <- count + 1 # sum 1 to the number of operations
    } 
  }
  return(count)
}

Examples using the function

We can use the examples presented before.

ksum_pairs(nums = c(1,2,3,4), k = 5)

## [1] 2

ksum_pairs(c(3,1,3,4,3),6)

## [1] 1

  1. This problem is originally from LeetCode, you can find it in Leetcode. ↩

  2. Email: jocastillo@colmex.mx. For more content visit my website: https://joelcastillo.netlify.app
    If you have any questions or suggestions, I’d be grateful to hear from you. ↩

  3. This solution is entirely my own work. It was developed using R version 4.4.1 (2024-06-14 ucrt). ↩