69. x 的平方根

#平方根的值一定在1，x之间，是一个有序数组
#那么就满足二分查找的条件
class Solution:
    def mySqrt(self, x: int) -> int:
        if x==0 or x==1:
            return x #0和1的算术平方根为1
        low,high,res = 1,x,-1 #初始化
        while low<=high:
            mid = (low+high)//2
            if mid*mid<=x:
                res = mid
                low=mid+1
            else:
                high=mid-1
        return res