LEETCODE 1552. 两球之间的磁力

class Solution(object):
    def maxDistance(self, position, m):
        """
        :type position: List[int]
        :type m: int
        :rtype: int
        """
        position.sort()
        # 1,position[-1]-position[0]
        start=1
        end=position[-1]-position[0]
        s=start
        e=end
        def valid(position,m,mid):
            count=1
            pre=position[0]
            for item in position:
                if item-pre>=mid:
                    count+=1
                    pre=item
                if count>=m:
                    return True
            return False
        while s<=e:
            mid=s+(e-s)/2    
            if valid(position,m,mid):
                s=mid+1
            else:
                e=mid-1 

        return e