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:
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¤ ¤
¤ ¤ Because the 3rd row is incomplete, we return 2.
Example 2:
n = 8 The coins can form the following rows:
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¤ ¤
¤ ¤ ¤
¤ ¤ Because the 4th row is incomplete, we return 3. 利用 x(x+1)/2 <= n 求得x = (sqrt(8*n+1) -1)/2 Code O(1)
class Solution:
def arrageCoins(self, n):
return (int(math.sqrt(8*n +1) -1)//2)