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leetcode - Max Points on a Line

2013-12-24 12:32  张汉生  阅读(256)  评论(0)    收藏  举报

 

 1 class Solution {
 2 public:
 3     int maxPoints(vector<Point> &points) {
 4         unsigned n = points.size();
 5         if (n <= 2)
 6             return n;
 7         unsigned maxLen = 2;
 8         unordered_map<int, unsigned> xLines;
 9         unordered_map<int, unsigned> yLines;
10         //consider situation of x and y;
11         for (auto iter = points.begin(); iter != points.end(); iter++){
12             if (xLines.find(iter->x) == xLines.end())
13                 xLines[iter->x] = 1;
14             else xLines[iter->x]++;
15             maxLen = maxLen >= xLines[iter->x] ? maxLen : xLines[iter->x];
16             if (yLines.find(iter->y) == yLines.end())
17                 yLines[iter->y] = 1;
18             else yLines[iter->y]++;
19             maxLen = maxLen >= yLines[iter->y] ? maxLen : yLines[iter->y];
20         }
21         vector<unordered_set<double> > slopes(n,unordered_set<double>());
22         for (unsigned i = 0; i < n - 1 && n-i>maxLen; i++){
23             unsigned startLen = 2;
24             for (unsigned j = i + 1; j <=n-1&&n-j+startLen-1>maxLen; j++){
25                 int dx = points[j].x - points[i].x;
26                 int dy = points[j].y - points[i].y;
27                 if (dx == 0 && dy == 0)
28                     startLen++;
29                 if (dx == 0 || dy == 0)
30                     continue;
31                 double sl = ((double)dy) / ((double)dx);
32                 if (slopes[j].find(sl) != slopes[j].end())
33                     continue;
34                 slopes[j].insert(sl);
35                 unsigned curLen = startLen;
36                 for (unsigned k = j + 1; k < n && curLen+n-k>maxLen; k++){
37                     int ddx = points[k].x - points[i].x;
38                     int ddy = points[k].y - points[i].y;
39                     if (ddx == 0 && ddy == 0)
40                         curLen++;
41                     if (ddx == 0 || ddy == 0)
42                         continue;
43                     double ssl = ((double)ddy) / ((double)ddx);
44                     if (ssl != sl)
45                         continue;
46                     curLen++;
47                     slopes[k].insert(sl);
48                 }
49                 maxLen = maxLen >= curLen ? maxLen : curLen;
50             }
51         }
52         return maxLen;
53     }
54 };