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:

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.

注意，这一题可以从图形的结构入手，减去每一层的个数，最后判断n的值，如果n的值是0，则证明最后一行是完整的，如果是负数，则证明倒数第二行是完整的，最后一行不完整。

class Solution {
public:
    int arrangeCoins(int n) {
      int i = 1;
      while(n>0)
      {
          n-=i;
          ++i;
      }
      if(n==0)
          return i-1;
      else
          return i-2;
    }
};