Arranging Coins

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.

问题描述

你有n个硬币，第k级台阶放k个硬币，比如第1级放1个硬币，第2级放2个硬币，请问这n个硬币可以按这种方式摆上几级台阶（纯白话翻译）

解法一：

思路：

数学问题，等差数列求和。。(1+k)k/2 = n….已知n求解k，用求根公式。。。

Code:

public class Solution {    public int arrangeCoins(int n) {        return (int)((-1 + Math.sqrt(1 + 8*(long)n))/2);    }}