You have a total of n coins that you want to form in a staircase shape, where every k-th row must have exactly k coins.
Given n, find the total number of full staircase rows that can be formed.
n is a non-negative integer and fits within the range of a 32-bit signed integer.
Example 1:
n = 5
The coins can form the following rows:
¤
¤ ¤
¤ ¤
Because the 3rd row is incomplete, we return 2.
Example 2:
n = 8
The coins can form the following rows:
¤
¤ ¤
¤ ¤ ¤
¤ ¤
Because the 4th row is incomplete, we return 3.
class Solution:
     def arrangeCoins(self, n):
         """
         :type n: int
         :rtype: int
         """
         return int((1+8*n)**0.5 - 1) // 2
class Solution:
     def arrangeCoins(self, n):
         """
         :type n: int
         :rtype: int
         """
         return int((1+8*n)**0.5 - 1) // 2