Leetcode：Increasing Triplet Subsequence

Increasing Triplet Subsequence

题目：

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.

代码：

class Solution {public:    bool increasingTriplet(vector<int>& nums) {        int n = nums.size();        int a = INT_MAX;        int b = INT_MAX;        for (int i = 0; i < n; i++)        {            if (nums[i] <= a)            {                a = nums[i];            }            else if (nums[i] <= b)            {                b = nums[i];            }            else            {                return true;            }        }        return false;    }};