[binary search - simple] sword finger offer II 072 take a square root

subject
Example 1:

Input : x = 4
Output : 2

Example 2:

Input : x = 8
Output : 2
explain : 8 The square root of is 2.82842…, Because the decimal part will be rounded off , So back 2

Tips :

0 <= x <= 231 - 1

Code
Execution time ：44 ms, In all Python3 Defeated in submission 64.22% Users of
Memory consumption ：14.8 MB, In all Python3 Defeated in submission 89.31% Users of
Pass the test case ：1017 / 1017

class Solution:
    def mySqrt(self, x: int) -> int:
        left,right=0,x
        while left<=right:
            mid=left+(right-left)//2
            if mid*mid==x:
                return mid
            elif mid*mid>x:
                right=mid-1
            else:
                left=mid+1        
        return right

【 Method 2】
Execution time ：40 ms, In all Python3 Defeated in submission 82.25% Users of
Memory consumption ：14.8 MB, In all Python3 Defeated in submission 96.10% Users of
Pass the test case ：1017 / 1017

class Solution:
    def mySqrt(self, x: int) -> int:
        left,right,ans=0,x,-1
        while left<=right:
            mid=left+(right-left)//2
            if mid*mid<=x:
                ans=mid
                left=mid+1
            else:
                right=mid-1
        return ans