'''

class Solution {

public:

bool increasingTriplet(vector<int>& nums) {

vector<int> ans;

for(int num : nums) {

auto t = lower_bound(ans.begin(), ans.end(), num);

if(t != ans.end())

*t = num;

else ans.push_back(num);

if(ans.size()==3) return true;

}

return false;

}

};

'''

when the size is 3, return true.the cost is O(n) time complexity and O(1) space complexity, right?