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.

第一直覺想到 fibonacci 但不知道要怎樣處理就算了

暴力解去算每層每層到底需要幾個

然後扣掉可以用的硬幣

如果可以用的硬幣少於這一層要用的硬幣

就 return 剩下的硬幣數量

Golang

func arrangeCoins(n int) int {
    if n == 0 {
        return 0
    }
    cur := 1
    rem := n - 1
    for (rem >= cur + 1) {
        cur+=1
        rem -= cur
    }
    return cur
}