334. Increasing Triplet Subsequence

Difficulty: Medium

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

1
arr[i] < arr[j] < arr[k]

given

1
0 ≤ i < j < k ≤ n-1

else return false.

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

Examples:

Given

1
[1, 2, 3, 4, 5]

,

return

1
true

.

Given

1
[5, 4, 3, 2, 1]

,

return

1
false

.

Solutions:

double cursors (min + second min)

C++ version

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