原题地址：https://oj.leetcode.com/problems/max-points-on-a-line/

题意：Given n points on a 2D plane, find the maximum number of points that lie on the same straight line.

解题思路：找到平面上在一条直线上最多的点。点在同一条直线上意味着这些点的斜率是一样的，那么可以考虑使用哈希表来解决，{斜率：[点1，点2]}这样的映射关系。这里有几个需要考虑的要点：1，有可能是斜率无穷大。2，有可能有相同的点，比如[(1,2),(1,2)]。

代码：

# Definition for a point
# class Point:
#     def __init__(self, a=0, b=0):
#         self.x = a
#         self.y = b

class Solution:
    # @param points, a list of Points
    # @return an integer
    def maxPoints(self, points):
        length = len(points)
        if length < 3: return length
        res = -1
        for i in range(length):
            slope = {'inf': 0}
            samePointsNum = 1
            for j in range(length):
                if i == j:
                    continue
                elif points[i].x == points[j].x and points[i].y != points[j].y:
                    slope['inf'] += 1
                elif points[i].x != points[j].x:
                    k = 1.0 * (points[i].y - points[j].y) / (points[i].x - points[j].x)
                    if k not in slope:
                        slope[k] = 1
                    else:
                        slope[k] += 1
                else:
                    samePointsNum += 1
            res = max(res, max(slope.values()) + samePointsNum)
        return res