Arranging Coins

Problem Statement - link #

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.

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.

Constraints #

• 1 <= n <= 2^31 - 1

Solutions #

class Solution {
public:
    int arrangeCoins(int n) {
      return int(sqrt(2*(long)n+0.25)-0.5);
    }
};