arranging_coins.py

class Solution:
    def arrangeCoins(self, n: int) -> int:
        left, right = 1, n
        while left <= right:
            mid = (right+left)//2
            num = (mid/2) * (mid+1)
            if num <= n:
                left = mid + 1
            else:
                right = mid - 1
        return right