This website contains ALL LeetCode **Premium** problems for
**FREE!!**.

All leaked interview problems are collected from Internet.

All leaked interview problems are collected from Internet.

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 existsi, j, k

such thatarr[i]<arr[j]<arr[k]given 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, 2, 3, 4, 5]`

,

return `true`

.

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

,

return `false`

.

**Credits:**

Special thanks to @DjangoUnchained for adding this problem and creating all test cases.

b''