LeetCode: Arranging Coins

LeetCode: Arranging Coins

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:

1
2
3
4
5
6
7
8
n = 5

The coins can form the following rows:
¤
¤ ¤
¤ ¤

Because the 3rd row is incomplete, we return 2.

Example 2:

1
2
3
4
5
6
7
8
9
n = 8

The coins can form the following rows:
¤
¤ ¤
¤ ¤ ¤
¤ ¤

Because the 4th row is incomplete, we return 3.
1
2
3
4
5
public class Solution {
    public int arrangeCoins(int n) {
        return ((int) Math.sqrt(1 + 8L * n) - 1) / 2;
    }
}