334. Increasing Triplet Subsequence

Given an unsorted array return whether an increasing subsequence of length 3 exists or not in the array.

Formally the function should:

Return true if there exists i, j, k such that arr[i] < arr[j] < arr[k] given 0 ≤ i < j < k ≤ n -1 else return false.

Note: Your algorithm should run in O( n ) time complexity and O( 1 ) space complexity.

Example 1:

Input: [1,2,3,4,5]
Output: true

Example 2:

Input: [5,4,3,2,1]
Output: false

# @lc code=start
using LeetCode

function increasing_triplet(nums::Vector{Int})
    fst_min = scd_min = nums[1]
    len = length(nums)
    idx = 2
    while idx <= len
        (nums[idx] != fst_min) && break
        idx += 1
    end
    (idx >= len) && return false
    fst_min, scd_min = minmax(fst_min, nums[idx])
    for num in @view(nums[(idx + 1):end])
        (num > scd_min) && return true
        scd_min = num
        fst_min, scd_min = minmax(fst_min, scd_min)
    end
    return false
end
# @lc code=end

increasing_triplet (generic function with 1 method)

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