[Solved] 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.

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.

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 <= 231 - 1

Python Solution

class Solution:
    def arrangeCoins(self, n: int) -> int:
        if n==1:
            return 1
        l=0
        r=n//2 + 1
        while l<=r:
            m = l+(r-l)//2
            x = (m*(m+1)//2)
            if x==n:
                return(m)
            elif x<n:
                l = m+1
            else:
                r=m-1
        return(l-1)