LeetCode OJ Max Points on a Line

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

刚开始着急了，没有想清楚情况，没有点，一个点，相同点，斜率不存在。。。

对于两个点建立直线方程，然后从头到尾查看是否有符合的点就行了，做的时候用了误差处理，不知道不用误差处理会不会错。。

class Solution {
public:
    int maxPoints(vector<Point> &points) {
        if (points.size() == 0) {
            return 0;
        }
        if (points.size() == 1) {
            return 1;
        }
        if (points.size() == 2) {
            return 2;
        }
        int max_num = 2;
        for (int i = 0; i < points.size(); i++) {
            for (int j = i + 1; j < points.size(); j++) {
                if (points[i].x == points[j].x) {  // the slope does not exist
                    int xx = points[i].x;
                    int counter = 0;
                    for (int q = 0; q < points.size(); q++) {
                        if (points[q].x == xx) {
                            counter++;
                        }
                    }
                    if (counter > max_num) {
                        max_num = counter;
                    }
                } else if (points[i].x != points[j].x) {
                    int counter = 0;
                    double k = (points[i].y * 1.0 - points[j].y) / (points[i].x * 1.0 - points[j].x);
                    double b = points[i].y - k * points[i].x;
                    for (int q = 0; q < points.size(); q++) {
                        double error = points[q].y - k * points[q].x - b;
                        if (-0.001 <= error && error <= 0.001) {
                            counter++;
                        }
                    }
                    if (counter > max_num) {
                        max_num = counter;
                    }
                }
            }
        }
        return max_num;
    }
};