334 Increasing Triplet Subsequence 1

Joel Castillo Espinosa 2

DESCRIPTION

Given an integer array nums, return true if there exists a triple of indices (i, j, k) such that i < j < k and nums[i] < nums[j] < nums[k]. If no such indices exists, return false.

Examples

  • Example 1:
    • Input: nums = [1,2,3,4,5]
    • Output: true
    • Explanation: Any triplet where i < j < k is valid.
  • Example 2:
    • Input: nums = [5,4,3,2,1]
    • Output: false
    • Explanation: No triplet exists.
  • Example 3:
    • Input: nums = [2,1,5,0,4,6]
    • Output: true
    • Explanation: The triplet (3, 4, 5) is valid because nums[3] == 0 < nums[4] == 4 < nums[5] == 6.

Constraints:

  • 1 ≤ nums.length ≤ $5*10^5$
  • $-2^{31}$ ≤ nums[i] ≤ $2^{31}$ - 1

SOLUTION 3

triple <- function(nums) {
  # possible triplets
  lxp <- length(nums) - 2 
  result <- FALSE
  for (i in 1:lxp)  {
    if(result == FALSE) {
      # in each iteration create a subvector
      vec_check <- nums[i:length(nums)]
      # there is i-elements > first element in the subvector
      vec_check <- vec_check[vec_check[1] < vec_check]
      lv = length(vec_check)
      # if at least 2 elements in the new vector -> check again
      if (lv > 1 ) {
        # repeating the first process
        for (i in 1:lv)  {
          if(result == FALSE) {
            vec_check1 <- vec_check[i:lv]
            vec_check1 <- vec_check1[vec_check1[1] < vec_check1]
            # if at least one element in the new vector -> condition is true
            result <-  ifelse(length(vec_check1) >= 1,TRUE,FALSE)
          } else {result <- TRUE} # maintain true 
        }
      }
    } else{result <- TRUE} # maintain true 
  }
  return(result)
}

Examples using the function

We can use the examples presented before.

triple(c(1,2,3,4,5))

## [1] TRUE

triple(nums = c(5,4,3,2,1))

## [1] FALSE

triple(c(2,1,5,0,4,6))

## [1] TRUE

  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). ↩