递归 python

↵一、简单理解

解决问题的一种方法，它将问题不断的分成更小的子问题，直到子问题可以用普通的方法解决。通常情况下，递归会使用一个不停调用自己的函数。

【注】：每一次递归调用都是在解决一个更小的问题，如此进行下去，直到问题本身不能在简化为止

例子：

1.列表元素之和

# 求列表元素之和
def sumList(numlist):'''循环计算列表和:param numlist:数值列表:return: 和'''sum = 0for num in numlist:sum += numreturn sumdef listnum(numlist):'''递归计算列表和:param numlist: 数值列表:return: 和'''if len(numlist) == 1:return numlist[0]else:return numlist[0] + listnum(numlist[1:])if __name__ == "__main__":numlist = [1, 2, 3, 4, 5, 6]a = sumList(numlist)b = listnum(numlist)print("循环计算结果：%f,递归计算结果：%f" % (a, b))

2.整数转换进制

# 将整数转换成以2-16为进制基数的字符串
def toStr(n, base):'''将输入的整数n转换成2-16任意进制的字符串:param n: 任意正整数:param base: 2-16中进制:return: 转换好的字符串'''convertString = "0123456789ABCDEF"if n < base:return convertString[n]else:return toStr(n // base, base) + convertString[n % base]if __name__ == "__main__":n = 10base = 2print("十进制数：%d 转换成二进制数：%s" % (n, toStr(n,base)))#字符的拼接

另外不使用字符拼接的方式

from main import Stack# 将整数转换成以2-16为进制基数的字符串
rStack = Stack()def toStr(n, base):'''将输入的整数n转换成2-16任意进制的字符串,不使用字符拼接，而是通过栈帧:param n: 任意正整数:param base: 2-16中进制:return: 转换好的数值存储栈帧'''convertString = "0123456789ABCDEF"if n < base:rStack.push(convertString[n])else:rStack.push(convertString[n % base])toStr(n // base, base)return rStackif __name__ == "__main__":n = 100base = 2numStack = toStr(n, base)print("整数%d转换为%d进制为：" % (n, base), end="")while numStack.size() >= 1:print(numStack.pop(), end="")

二、可视化

使用python中的画图工具进行简单递归程序的绘画，从而理解递归的概念

1.螺旋线

#用turtle模块递归的绘制螺旋线
from turtle import *myTurtle = Turtle()
myWin = myTurtle.getscreen()def drawSpiral(myTurtle, lineLen):if lineLen > 0:myTurtle.forward(lineLen)myTurtle.right(90)drawSpiral(myTurtle, lineLen - 5)drawSpiral(myTurtle, 100)
myWin.exitonclick()#用户在窗口内再次点击之后，程序清理并退出

2.分形树

#无法绘画出来的
from turtle import *myTurtle = Turtle()
myWin = myTurtle.getscreen()def tree(brancheLen, t):if brancheLen > 5:t.forward(brancheLen)t.right(20)tree(brancheLen-15,t)t.left(40)tree(brancheLen-10,t)t.right(20)t.backward(brancheLen)t = Turtle()
myWin = t.getscreen()
t.left(90)
t.up()
t.backward(100)
t.down
tree(110,t)
myWin.exitonclick()

chatGPT中给的代码

#能绘画出来
import turtledef draw_branch(t, length):if length > 5:t.forward(length)  # 绘制主干t.right(20)  # 右转一定角度draw_branch(t, length - 15)  # 递归绘制右侧分支t.left(40)  # 左转一定角度draw_branch(t, length - 15)  # 递归绘制左侧分支t.right(20)  # 右转一定角度t.backward(length)  # 返回原点def main():# 设置窗口和画笔window = turtle.Screen()window.bgcolor("white")t = turtle.Turtle()t.speed(0)  # 设置绘制速度为最快# 调整画笔位置和方向t.left(90)t.up()t.backward(200)t.down()# 绘制分形树draw_branch(t, 100)# 等待用户点击关闭窗口turtle.mainloop()if __name__ == "__main__":main()

3.谢尔平斯基三角形

chatGPT所给的代码---可运行

import turtledef draw_triangle(t, order, size):if order == 0:for _ in range(3):t.forward(size)t.left(120)else:draw_triangle(t, order - 1, size / 2)t.forward(size / 2)draw_triangle(t, order - 1, size / 2)t.backward(size / 2)t.left(60)t.forward(size / 2)t.right(60)draw_triangle(t, order - 1, size / 2)t.left(60)t.backward(size / 2)t.right(60)def main():# 设置窗口和画笔window = turtle.Screen()window.bgcolor("white")t = turtle.Turtle()t.speed(0)  # 设置绘制速度为最快# 调整画笔位置和方向t.up()t.goto(-200, -150)t.down()# 绘制谢尔平斯基三角形draw_triangle(t, 5, 400)# 隐藏画笔t.hideturtle()# 等待用户点击关闭窗口turtle.mainloop()if __name__ == "__main__":main()

b站上所学

# 绘制谢尔平斯基三角形
#B站--python递归三部曲（基于turtle实现可视化）
import turtlet = turtle.Turtle()def get_midpoint(a, b):'''得到两点的中点坐标:param a: 坐标点（元组）:param b: 坐标点（元组）:return: 中点坐标（元组）'''ax, ay = abx, by = breturn ((ax + bx) / 2, (ay + by) / 2)def draw_triangle(a, b, c):'''绘制以a，b，c为顶点的三角形:param a: 顶点坐标（元组）:param b: 顶点坐标（元组）:param c: 顶点坐标（元组）:return: 无返回值'''ax, ay = abx, by = bcx, cy = ct.penup()  # 提起画笔t.goto(a)  # 画笔移动到a点的位置t.pendown()  # 落下画笔t.goto(b)  # 画出ab线段t.goto(c)  # 画出bc线段t.goto(a)  # 画出ca线段t.penup()def draw_sierpinski(triangle, depth):a, b, c = triangle  # triangle包括三个顶点的元组draw_triangle(a, b, c)if depth == 0:returnelse:d = get_midpoint(a, b)e = get_midpoint(b, c)f = get_midpoint(c, a)adf = (a, d, f)dbe = (d, b, e)fec = (f, e, c)draw_sierpinski(adf, depth - 1)draw_sierpinski(dbe, depth - 1)draw_sierpinski(fec, depth - 1)if __name__ == "__main__":triangle = ((-200,-100),(0,200),(200,-100))draw_sierpinski(triangle,4)

4.汉诺塔

不能可视化的

#B站---python递归三部曲（基于turtle实现可视化）
#汉诺塔
def moveDisk(diskIndex,fromPole,toPole):'''从起始塔向目标塔移动圆环:param diskIndex:圆环:param fromPole:起始塔:param toPole:目标塔:return:无'''print_str = 'Move disk %s from %s to %s' %(diskIndex,fromPole,toPole)print(print_str)def moveTower(height,fromPole,withPole,toPole):'''汉诺塔的递归调用函数:param height: 汉诺塔高度:param fromPole: 起始塔:param withPole: 中转塔:param toPole: 目标塔:return:'''if height == 1:moveDisk(1,fromPole,toPole)else:moveTower(height-1,fromPole,toPole,withPole)moveDisk(height,fromPole,toPole)moveTower(height-1,withPole,fromPole,toPole)if __name__ == "__main__":moveTower(3,"A","B","C")

能可视化的

#自己对着B站视频写的一半，但是无法正确跑，不过注释都是正确的意思
import turtledef set_plate(i):'''绘制第i层圆盘:return:'''size = 20  # 圆盘转弯半径基数l = size * (i + 2)  # 第i层圆盘半径t = turtle.Turtle()t.hideturtle()  # 隐藏画笔t.penup()  # 提起画笔t.left(90)  # 每次先逆时针旋转90度，新建的左转90度为设置时的图案。t.begin_poly()  # 绘制记录t.forward(l)  # 向前走40t.circle(size, 180)  # 画一个半径为20，角度为180的弧t.forward(l * 2)t.circle(size, 180)t.forward(l)t.end_poly()  # 结束记录turtle.register_shape("plate_%s" % i, p)  # 取出记录的情况，给不同层的圆盘赋值不同的名称def set_tower():'''绘制塔:return:'''# 塔的参数：宽、高、转弯半径tower_width = 100tower_height = 200tower_radius = 10t = turtle.Turtle()t.hideturtle()  # 隐藏画笔t.penup()  # 提起画笔t.left(90)t.begin_poly()t.forward(tower_width)t.circle(tower_radius, 180)t.forward(tower_width - tower_radius)t.right(90)t.forward(tower_height)t.circle(tower_radius, 180)t.forward(tower_height)t.right(90)t.forward(tower_width - tower_radius)t.circle(tower_radius, 180)t.forward(tower_width)t.end_poly()turtle.register_shape("tower")def draw_towers():# 塔的参数：塔之间的距离，塔的海拔高度tower_distance = 250tower_altitude = -100set_tower()tower = turtle.Turtle("tower")tower.speed(0)  # 0是最快的速度tower.penup()tower.goto(-tower_distance, tower_altitude)  # 移动到（-250，-100）位置tower.stamp()  # 一直显示出来tower.goto(0, tower_altitude)tower.stamp()tower.goto(tower_distance, tower_altitude)if __name__ == "__main__":draw_towers()set_plate(1)plate = turtle.Turtle("plate_1")plate.forward(200)turtle.done()

B站博主所写代码参考网址：需要魔法（可参考网络代理文章）

#能可视化代码，但是turtle库的绘制方法不熟悉
import turtle# ==============
#  常量设置
# ==============
N = 7  # 汉诺塔层数限制BasePL = 12  # plate的大小基数，修改这个能够调整plate的大小
TowerP = 5  # Tower的线宽
TowerW = 110  # Tower的底座宽度
TowerH = 200  # Tower的高度
TowerSpace = 260  # Tower的之间的距离，从中心到中心
HORIZON = -100  # Tower的底座高度，用于定位
# 动画速度，5是比较适中的速度
PMS = 5# 优化处理
Isjump = TruePOLES = {"1": [],"2": [],"3": [],
}
PLATES = []  # 存储所有圆盘对象# 塔的颜色
LineColor = "black"
# 多个盘子的颜色
FillColors = ["#d25b6a","#d2835b","#e5e234","#83d05d","#2862d2","#35b1c0","#5835c0"
]
# 建立窗体
SCR = turtle.Screen()
# SCR.tracer()
SCR.setup(800, 600)  # 设置窗体大小# 设置圆盘形状
def set_plate(pi=0):_pi = pi + 2t = turtle.Turtle()t.hideturtle()t.speed(0)t.penup()t.begin_poly()t.left(90)t.forward(BasePL * _pi)t.circle(BasePL, 180)t.forward(BasePL * 2 * _pi)t.circle(BasePL, 180)t.forward(BasePL * _pi)t.end_poly()p = t.get_poly()pname = 'plate_%s' % piSCR.register_shape(pname, p)# 设置塔柱形状
def set_tower():t = turtle.Turtle()t.hideturtle()t.speed(0)t.penup()t.begin_poly()t.left(90)t.forward(TowerW)t.circle(-TowerP, 180)t.forward(TowerW)t.forward(TowerW)t.circle(-TowerP, 180)t.forward(TowerW - TowerP / 2)t.left(90)t.forward(TowerH)t.circle(-TowerP, 180)t.forward(TowerH)t.end_poly()p = t.get_poly()SCR.register_shape('tower', p)# 绘制塔柱
def draw_towers():set_tower()for tx in [-TowerSpace, 0, TowerSpace]:t3 = turtle.Turtle('tower')t3.penup()t3.goto(tx, HORIZON)# 绘制圆盘
def draw_plates(pn=4):plates = []for i in range(pn):set_plate(i)_plate = 'plate_%s' % i_p = turtle.Turtle(_plate)_colorIdx = i % len(FillColors)_color = FillColors[_colorIdx]_p.color(_color, _color)_p.speed(PMS)plates.append(_p)# 反序，大的在前，小的在后global PLATESPLATES = plates[:]# 绘制移动过程
def draw_move(diskIndex, fromPindex, toPindex):p = PLATES[diskIndex - 1]index_loc = {"A": 1,"B": 2,"C": 3}toP = index_loc.get(toPindex, None)fromP = index_loc.get(fromPindex, None)p.penup()mx = (toP - 2) * TowerSpacemy = HORIZON + len(POLES[str(toP)]) * BasePL * 2if fromP != None:POLES[str(fromP)].remove(p)if Isjump:px, py = p.pos()p.goto(px, TowerH + py)p.goto(mx, TowerH + py)p.goto(mx, my)POLES[str(toP)].append(p)# 将所有圆盘移动到起点
def movetoA(n, fromPindex):for i in range(n, 0, -1):draw_move(i, None, fromPindex)# 移动指定层圆盘diskIndex，从fromPole出发，到达toPole
def moveDisk(diskIndex, fromPole, toPole):""":param diskIndex: 圆盘的索引（从上往下，第一层为1，第二层为2、、、第n层为n）:param fromPole: 出发的柱子（起点）:param toPole: 要到达的柱子（终点）:return:"""draw_move(diskIndex, fromPole, toPole)# 核心函数，入口
def moveTower(height, fromPole, withPole, toPole):""":param height: 汉诺塔高度——层数:param fromPole: 出发的柱子（起点）:param withPole: 进过的柱子（中转点）:param toPole: 要到达的柱子（终点）:return:"""if height == 1:# 基础情形：一层的汉诺塔moveDisk(1, fromPole, toPole)return# 先将圆盘1到n - 1看作一个整体从起点塔移动到中转塔（用目标塔作为本步骤的中转）moveTower(height - 1, fromPole, toPole, withPole)# 再将圆盘n从起点塔A移动到目标塔CmoveDisk(height, fromPole, toPole)# 最后将圆盘1到n - 1看作一个整体从中转塔移动到目标塔（用起点塔作为本步骤的中转）moveTower(height - 1, withPole, fromPole, toPole)if __name__ == '__main__':# 调用# 三层汉诺塔，A为出发柱子，B为中转柱子，C为目标柱子n = NSCR.tracer(0)draw_towers()draw_plates(n)movetoA(n, "A")SCR.tracer(1)# SCR.delay(3)moveTower(n, "A", "B", "C")turtle.done()