Hold住Leetcode——Arranging Coins

题目的意思是：
给一个整数，将其分解成从1开始连续的几个数相加，返回那个最大的数。能用数学的先验知识解决的就不要麻烦计算机去做，这样才能最快！n = 5


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


Because the 3rd row is incomplete, we return 2.
n = 8


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


Because the 4th row is incomplete, we return 3.
设最大值是a，a满足（1+a）*a/2<=n,找出满足条件的最大的a。

class Solution {public: 
int arrangeCoins(int n) {

        if(n==0)
        return 0;
         int a;
      a=(int)(sqrt((double)2*n+0.25)-0.5);
        return a;
    }
};