Triangle - 1point3acres


https://www.1point3acres.com/bbs/forum.php?mod=viewthread&tid=207550&extra=&page=1题目没法描述,哪天画个图片再贴上来,和图形有关的,三角形套三角形,问怎么输出一堆点,然后用已知的画线api生成某一depth的图形,不知道以前面经里有没有这道题。然后就是一直没思路,问hint也没什么有用信息,三哥就说写个简单的情况,然后突然想出点思路,然后三哥一直抠细节,问的心烦,一会问这一会问那,根本没法思考,然后看着电脑的时间不多了,心态也不好了,最后代码就写了一点点,心里当时已经是死灰一片,最后和他repeat了一下思路,貌似之前他还没有理解我要干什么,最后问他怎么做,说我on the right track。出来后感觉三哥就是个坑,占用那么多时间说其他的


输入三个顶点和depth. check 1point3acres for more.
输出一堆点
问somehow,用这些点两两连线把depth的图画出来



画三角形那道题可不可以理解为level order traversal 的变种,bfs那种的。据我观察,每加深一层,就是把一个当前的三角形分成三个三角形(中间的倒三角形不算,这样画出的边也没有重合)写了一下代码,constructor没有详写

  1. public class Point {
  2.         int x, y;
  3.         public Point() {}
  4. }
  5. public class Triangle {
  6.         Point A, B, C;
  7.         public Triangle(Point A, Point B, Point C){}
  8. }
  9. public Point getMid(Point A, Point B) {
  10.         int x = (A.x + B.x) / 2, y = (A.y + B.y) / 2; //不考虑double的情况
  11.         return new Point(x, y);
  12. }

  13. public void drawLine(Point A, Point B) {}
  14. public void drawTri(Triangle tri) {
  15.         drawLine(tri.A, tri.B);
  16.         drawLine(tri.B, tri.C);
  17.         drawLine(tri.A, tri.C);
  18. }
  19. public void drawGraph(Point A, Point B, Point C, int depth) {
  20.         Triangle basic = new Triangle(A, B, C);
  21.         Queue<Triangle> q = new LinkedList<Triangle>();
  22.         q.offer(basic);
  23.         for(int i = 0; i < depth; i++) {
  24.                 int size = q.size();
  25.                 for(int j = 0; j < size; j++) {
  26.                         basic = q.poll();
  27.                         Point mid_AB = getMid(basic.A, basic.B);
  28.                         Point mid_AC = getMid(basic.A, basic.C);
  29.                         Point mid_BC = getMid(basic.B, basic.C);
  30.                         q.offer(new Triangle(basic.A, mid_AC, mid_AB));
  31.                         q.offer(new Triangle(basic.B, mid_BC, mid_AB));
  32.                         q.offer(new Triangle(basic.C, mid_BC, mid_AC));
  33.                 }. check 1point3acres for more.
  34.         }
  35.         while(!q.isEmpty()) {. check 1point3acres for more.
  36.                 drawTri(q.poll());
  37.         }
  38. }

  1. class Point(object):
  2.     def __init__(self, x, y):
  3.         self.x = x
  4.         self.y = y


  5. def draw_line(p1, p2):
  6.     ninja.penup()
  7.     ninja.goto(p1.x, p1.y)
  8.     ninja.pendown()
  9.     ninja.goto(p2.x, p2.y)


  10. def draw_trangle(p1, p2, p3):
  11.     draw_line(p1, p2)
  12.     draw_line(p2, p3)
  13.     draw_line(p3, p1)


  14. def dfs(p1, p2, p3, depth):
  15.     draw_trangle(p1, p2, p3)
  16.     if depth:
  17.         m1 = Point((p1.x+p2.x)/2., (p1.y+p2.y)/2.)
  18.         m2 = Point((p2.x+p3.x)/2., (p2.y+p3.y)/2.)
  19.         m3 = Point((p3.x+p1.x)/2., (p3.y+p1.y)/2.)
  20.         depth -= 1
  21.         dfs(p1, m1, m3, depth)
  22.         dfs(p2, m1, m2, depth)
  23.         dfs(p3, m2, m3, depth)

我估计应该是这个意思:假设给定一个类似于“void drawLine(const Pt& p1, const Pt& p2)”的API,我也是用的recursion.

我想的办法是构建一个类似金字塔的点阵,depth增加的时候插入新的一层点阵并按照规律画线,不过显然层主的这个方法好多了

  1. typedef pair<double,double> Pt;. check 1point3acres for more.
  2. typedef vector<Pt> Tri;
  3. typedef vector<Tri> Tris;

  4. // assumed given API. check 1point3acres for more.
  5. void drawLine(const Pt& p1, const Pt& p2); 

  6. // utility function to draw a given triangle
  7. void drawTri(const Tri& tri) {
  8.   for (int i = 0; i < 3; i++) drawLine(tri[i%3], tri[(i+1)%3]);
  9. }

  10. // dfs routine to draw central triangle and collect 
  11. // 4 smaller triangles for each big trianlges
  12. Tris dfs(const Tris& tris) {
  13.   Tris res;    -baidu 1point3acres
  14.   for (const auto& t:tris) {
  15.     drawTri(t); Tri tri;
  16.     // construct and draw central triangle
  17.     for (int i = 0; i < 3; i++)
  18.       tri.push_back(Pt((t[i%3].first+t[(i+1)%3].first)/2.0,(t[i%3].second+t[(i+1)%3].second)/2.0));
  19.     drawTri(tri);
  20.     // collect all 4 smaller triangles into result
  21.     res.push_back(tri);    
  22.     for (int i = 0; i < 3; i++) {
  23.       res.push_back({t[i], res[0][i], res[0][(i+2)%3]});
  24.     }
  25.   } 
  26.   return res;
  27. }
  28. . 1point3acres
  29. // main function to draw triangles with given depth
  30. void drawTriangles(const Tri& tri, unsigned int depth) {
  31.   Tris tris = { tri };
  32.   while (depth-- > 0) tris = dfs(tris);
  33. }

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