[LeetCode]Max Points on a Line

最新推荐文章于 2019-10-13 11:03:53 发布

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本文介绍了一种高效算法，用于解决给定点集中最大共线点数的问题。通过遍历每一对点计算斜率并使用哈希表记录斜率出现频率，找出具有最多共线点的直线。

/**
 * 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 globalMaxPointInLineNum = 0;
        //for each point x in the set A
        for(int i = 0; i < points.size(); ++i)
        {
            int samePtNum = 0;
            int localMaxPointInLineNum = 0;
            std::unordered_map<double, int> hashCntTable;
            //for each point y (not equal x) in the set A
            for(int j = i+1; j < points.size(); ++j)
            {
                double slope = std::numeric_limits<double>::infinity();//positive infinity
                //judge if they are the same point
                if(points[i].x == points[j].x && points[i].y == points[j].y)
                {
                    samePtNum++;
                    continue;
                }
                //if they have the slope, recompute their slope
                if(points[i].x != points[j].x)
                {
                    slope = (double)(points[i].y-points[j].y)/(double)(points[i].x-points[j].x);
                }
                //save the slope in the hash count table
                hashCntTable[slope]++;
                //keep record of the local max
                localMaxPointInLineNum = std::max(localMaxPointInLineNum, hashCntTable[slope]);
            }
            //keep record of the global max
            globalMaxPointInLineNum = std::max(globalMaxPointInLineNum, localMaxPointInLineNum+samePtNum+1);
        }
        return globalMaxPointInLineNum;
    }
    
};