C++ python高斯小學公式解Leetcode 1759 Count Number of Homogenous Substrings

C++ python高斯小學公式解Leetcode 1759  Count Number of Homogenous Substrings

高斯小學公式解1+2+...+n=n(n+1)/2 就 O(1)時間，不用它也行改用迴圈需時O(n)。解Leetcode 1759. Count Number of Homogenous Substrings也很好用，O(n)時間，O(1)空間，如果還要優化，就考慮平行化，這裡似乎有難度，空間就多用點。

[codes on Leetcode]https://leetcode.com/problems/count-number-of-homogenous-substrings/solutions/4266521/c-python-sum-of-n-n-1-2-0-ms-beats-100/

[Leetcode playList]https://www.youtube.com/watch?v=odbN3KooN8s&list=PLYRlUBnWnd5IdDHk2BjqXwesydU17z_xk