Aizu - ALDS1_5_C 递归+几何推导

Koch Curve

Write a program which reads an integer n and draws a Koch curve based on recursive calles of depth n.

The Koch curve is well known as a kind of fractals.

You can draw a Koch curve in the following algorithm:

• Divide a given segment (p1, p2) into three equal segments.
• Replace the middle segment by the two sides of an equilateral triangle (s, u, t) of the same length as the segment.
• Repeat this procedure recursively for new segments (p1, s), (s, u), (u, t), (t, p2).

You should start (0, 0), (100, 0) as the first segment.

Input

An integer n is given.

Output

Print each point (x, y) of the Koch curve. Print a point in a line. You should start the point(0, 0), which is the endpoint of the first segment and end with the point (100, 0), the other endpoint so that you can draw the Koch curve as an unbroken line. Each solution should be given as a decimal with an arbitrary number of fractional digits, and with an absolute error of at most 10-4.

Constraints

• 0 ≤ n ≤ 6

Sample Input 1

1

Sample Output 1

0.00000000 0.00000000
33.33333333 0.00000000
50.00000000 28.86751346
66.66666667 0.00000000
100.00000000 0.00000000

Sample Input 2

2

Sample Output 2

0.00000000 0.00000000
11.11111111 0.00000000
16.66666667 9.62250449
22.22222222 0.00000000
33.33333333 0.00000000
38.88888889 9.62250449
33.33333333 19.24500897
44.44444444 19.24500897
50.00000000 28.86751346
55.55555556 19.24500897
66.66666667 19.24500897
61.11111111 9.62250449
66.66666667 0.00000000
77.77777778 0.00000000
83.33333333 9.62250449
88.88888889 0.00000000
100.00000000 0.00000000


思路：递归控制输出，点坐标几何推导，关于旋转矩阵相关内容参看博客：https://www.cnblogs.com/zhoug2020/p/7842808.html，写的很详细。


电子板写的，手感很差，凑合看吧，这个过程是得出是s，u，t三点坐标的；

Code

//Aizu - ALDS1_5_C
#include <bits/stdc++.h>

using namespace std;

const double pi = acos(-1);

void koch(int n, pair<double, double> p1, pair<double, double> p2)
{
    if (n == 0) return;

    double th = pi * 60.0 / 180.0;
    pair<double, double> s, u, t;

    s.first = (2.0 * p1.first + p2.first) / 3.0;
    s.second = (2.0 * p1.second + p2.second) / 3.0;

    t.first = (p1.first + 2.0 * p2.first) / 3.0;
    t.second = (p1.second + 2.0 * p2.second) / 3.0;

    u.first = cos(th) * (t.first - s.first) - sin(th) * (t.second - s.second) + s.first;
    u.second = sin(th) * (t.first - s.first) + cos(th) * (t.second - s.second) + s.second;

    koch(n - 1, p1, s);
    printf("%.8lf %.8lf\n", s.first, s.second);
    koch(n - 1, s, u);
    printf("%.8lf %.8lf\n", u.first, u.second);
    koch(n - 1, u, t);
    printf("%.8lf %.8lf\n", t.first, t.second);
    koch(n - 1, t, p2);
}

int main()
{
    int n;
    cin >> n;
    printf("%.8lf %.8lf\n", 0.0, 0.0);
    koch(n, make_pair(0.0, 0.0), make_pair(100.0, 0.0));
    printf("%.8lf %.8lf\n", 100.0, 0.0);
    return 0;
}