leetcode: Max Points on a Line

最新推荐文章于 2019-01-11 00:33:51 发布

martin_liang

最新推荐文章于 2019-01-11 00:33:51 发布

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分类专栏： C++/C 算法 leetcode

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本文介绍了一个算法问题：给定平面上的n个点，如何找出处于同一直线上的最大数量的点。通过计算每两点之间的斜率并进行统计，可以找到最多共线点的数量。

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

/**
 * 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 pointsNum = points.size();
        if (pointsNum == 0)
            return 0;
        
        int maxPointsForSlope = 1;
        
        for (int i=0; i<pointsNum-1; i++)
        {
            map<double, int> curPointSlopeMap;
            int samePoints = 0;
            int curPointMaxSlope = 1;
            
            for (int j=i+1; j<pointsNum; j++)
            {
                double slope = std::numeric_limits<double>::infinity();
                
                if (points[i].x != points[j].x)
                {
                    slope = 1.0*(points[i].y - points[j].y) / (points[i].x - points[j].x);
                }
                else if (points[i].y == points[j].y)
                {
                    samePoints++;
                    continue;
                }
                
                if (curPointSlopeMap.count(slope) != 0)
                {
                    curPointSlopeMap[slope]++;
                }
                else
                {
                    curPointSlopeMap[slope] = 2;
                }
                
                if (curPointSlopeMap[slope] > curPointMaxSlope)
                {
                    curPointMaxSlope = curPointSlopeMap[slope];
                }
            }
            if (curPointMaxSlope + samePoints > maxPointsForSlope)
                maxPointsForSlope = curPointMaxSlope + samePoints;
        }
        
        return maxPointsForSlope;
        
    }
};