第八周：(LeetCode 441) Arranging Coins（c++）

原题：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.

思路：这是一道二分查找的简单题。由于上周写了个二分查找的变种写的不是很顺，所以这周专门找了一道二分查找的题来做做。这题要特别注意如果直接用int会有溢出的问题。

代码如下：

class Solution {public:    int arrangeCoins(int n) {        long long high=n,low=0,mid,result;        while(low<=high){            mid=(high-low)/2+low;            result=(mid+1)*mid/2;            if(result>n){                high=mid-1;             }else if(result<n){                low=mid+1;            }else{                return mid;            }        }        return high;    }};