LeetCode----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.

分析： 任取两点组成的直线，看有多少点在其上面。

注意： 考虑 3 种情况： 两点重合； 斜率为无穷大； 正常情况

/**
 * Definition for a point.
 * struct Point {
 *     int x;
 *     int y;
 *     Point() : x(0), y(0) {}
 *     Point(int a, int b) : x(a), y(b) {}
 * };
 */
class Solution {
public:
    int maxPoints(vector<Point> &points) {
        int max_points(0);
        double a(0), b(0); // denote a straight line
        LINE_TYPE line_type(LINE); 
        
        if(points.size() == 0) return 0;
        else if(points.size() == 1) return 1;
        
        for(int i=0; i<points.size(); ++i)
          for(int j=i+1; j<points.size(); ++j)
          {
              if(points[i].x == points[j].x){
                  if(points[i].y == points[j].y)
                    line_type = POINT;
                  else
                    line_type = VLINE;
              }
              else{
                line_type = LINE;
                a = (points[j].y - points[i].y) / static_cast<double>(points[j].x - points[i].x); //tangent
                b = points[i].y - a * points[i].x;
              }
              
              // compute how many points on the line  
              int point_count(2);
              for(int k=0; k<points.size(); ++k){
                if(k == i || k == j) continue;
                
                // test whether points[k] on the line
                if(line_type == LINE){
                    if( fabs(points[k].y - a*points[k].x - b) < 1e-10)
                      ++ point_count;
                }
                else if(line_type == POINT){
                    if(points[k].x == points[i].x && points[k].y == points[i].y)
                        ++ point_count;
                }
                else{
                    if(points[k].x == points[i].x)
                        ++ point_count;
                }
              }
              max_points = max(max_points, point_count);
          }
        
        return max_points;
    }
private:
    enum LINE_TYPE{POINT, LINE, VLINE}; 
};

LeetCode----Max Points On a Line

原文：http://blog.csdn.net/shoulinjun/article/details/19152791