# 441. Arranging Coins

## 1. Question

You have n coins and you want to build a staircase with these coins. The staircase consists of k rows where the ith row has exactly i coins. The last row of the staircase may be incomplete.

Given the integer n, return the number of complete rows of the staircase you will build.

## 2. Examples

Example 1:

Input: n = 5
Output: 2
Explanation: Because the 3rd row is incomplete, we return 2.


Example 2:

Input: n = 8
Output: 3
Explanation: Because the 4th row is incomplete, we return 3.


## 3. Constraints

• 1 <= n <= 231 - 1

## 5. Solutions

class Solution {
public int arrangeCoins(int n) {
if(n <= 1) {
return n;
}
long sum = 2 * (long)n;
System.out.println(sum);
long ans = 1;
while (ans * (ans + 1) <= sum) {
ans++;
}
return (int) --ans;
}
}


class Solution {
public int arrangeCoins(int n) {
return (int) ((Math.sqrt((long) 8 * n + 1) - 1) / 2);
}
}