Description
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.
Solution
Math, time O(1)
利用二次方程求解公式：
image.png
注意要将n cast to long，否则8 * n会overflow！
class Solution {
public int arrangeCoins(int n) {
return (int) (Math.sqrt(1 + 8 * (long) n) - 1) / 2;
}
}
