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.
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.

class Solution {
public:
    bool increasingTriplet(vector<int>& nums) {
        int t1 = INT_MAX;
        int t2 = INT_MAX;
        for(int i=0;i<nums.size();i++){
            if(nums[i]<=t1){
                t1=nums[i];
            }else if(nums[i]<=t2){//巧用ELSE语句，即找到比第一个数T1大的
                t2=nums[i];
            }else{               //找到比t1,t2都大的返回true
                return true;
            }
        }
        return false;
    }
};