441. 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:

n = 5The coins can form the following rows:¤¤ ¤¤ ¤Because the 3rd row is incomplete, we return 2.

Example 2:

n = 8The coins can form the following rows:¤¤ ¤¤ ¤ ¤¤ ¤Because the 4th row is incomplete, we return 3.

题目大意：给定一个数字n，按照第k行放k个硬币的方法，硬币能摆成几行

现在假设能摆成k行，现在求不等式k*(k+1)/2<=n，如果是等号的话，k=Math.sqrt(2*n+1/4)-1/2,因为k是整数，令k=(int)Math.sqrt(2*n)，所以若不等式成立，

则返回k，若不成立，即k*(k+1)/2>n，则返回结果为k-1，代码如下：

        long l = n;        long k= (int) (Math.sqrt(2*l));        if(k*(k+1)/2<=l){        return (int) k;        }        else return (int) (k-1);