[binary search - simple] 441 Arrange coins

【 subject 】
【 Code 】
Execution time ：40 ms, In all Python3 Defeated in submission 82.23% Users of
Memory consumption ：14.8 MB, In all Python3 Defeated in submission 93.27% Users of
Pass the test case ：1335 / 1335

class Solution:
    def arrangeCoins(self, n: int) -> int:
        def cal(n):
            return (1+n)*n//2   
        line1=1
        linen=n
        while line1<=linen:
            mid=line1+(linen-line1)//2
            if cal(mid)==n:
                return mid
            elif cal(mid)<n:
                line1=mid+1
            elif cal(mid)>n:
                linen=mid-1
        return line1-1

class Solution:
    def arrangeCoins(self, n: int) -> int:
        def cal(n):
            return (1+n)*n//2   
        line1=1
        linen=n
        while line1<=linen:
            mid=line1+(linen-line1)//2
            if cal(mid)==n:
                return mid
            elif cal(mid)<n:
                line1=mid+1
            elif cal(mid)>n:
                linen=mid-1
        return linen