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.

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:

思路：碰到比小的就更新。参考discussion

public class Solution {    public boolean increasingTriplet(int[] nums) {        int small=Integer.MAX_VALUE;        int big=Integer.MAX_VALUE;        for(int m:nums){            if(m<=small){                small=m;            }else if(m<=big){                big=m;            }else{                return true;            }        }        return false;    }}

334. Increasing Triplet Subsequence