贪心算法

贪心算法

一.硬币找零

from IPython.display import Image
Image(filename="./data/7_01.png",width=800,height=960)

Image(filename="./data/7_02.png",width=800,height=960)

d=[0.05,0.1,0.2,0.5,1,2]
d_num=[]
s=0

temp=input("请输入每种零钱的数量：")
d_num0=temp.split(" ")

for i in range(0,len(d_num0)):
    d_num.append(int(d_num0[i]))
    s+=d[i]*d_num[i]
    
sum=float(input("请输入需要找的零钱："))
if sum>s:
    print("数据有误")

s=s-sum

i=5

while i>=0:
    if sum>=d[i]:
        n=int(sum/d[i])
        if n>=d_num[i]:
            n=d_num[i]
        sum-=n*d[i]
        print("用了%d个%f元硬币"%(n,d[i]))
    i-=1

请输入每种零钱的数量： 10 10 10 10 10 10
请输入需要找的零钱： 0.55


用了1个0.500000元硬币
用了1个0.050000元硬币

二.活动安排

Image(filename="./data/7_03.png",width=800,height=960)

# 冒泡排序
def bubble_sort(s,f):
    for i in range(len(f)):
        for j in range(0,len(f)-i-1):
            if f[j]>f[j+1]:
                f[j],f[j+1]=f[j+1],f[j]
                s[j],s[j+1]=s[j+1],s[j]
                
    return s,f

def greedy(s,f,n):
    a=[True for x in range(n)]
    
    j=0
    for i in range(1,n):
        if s[i]>=f[j]:
            a[i]=True
            j=i
        else:
            a[i]=False
            
    return a

n=int(input("活动总数："))
arr=input("活动序列：").split()

s=[]
f=[]

for ar in arr:
    ar=ar[1:-1]
    start=int(ar.split(",")[0])
    end=int(ar.split(",")[1])
    s.append(start)
    f.append(end)
    
s,f=bubble_sort(s,f)
A=greedy(s,f,n)

res=[]
for k in range(len(A)):
    if A[k]:
        res.append("({},{})".format(s[k],f[k]))
        
print(" ".join(res))

活动总数： 3
活动序列： [0,5] [5,10] [3,7]


(0,5) (5,10)

三.哈夫曼编码

Image(filename="./data/7_04.png",width=800,height=960)

Image(filename="./data/7_05.png",width=800,height=960)

class Node(object):
    def __init__(self,freq):
        self.left=None
        self.right=None
        self.father=None
        self.freq=freq
        
    def isLeft(self):
        return self.father.left==self
    
def createNodes(freqs):
    return [Node(freq) for freq in freqs]

def createHuffmanTree(nodes):
    queue=nodes[:]
    
    while len(queue)>1:
        queue.sort(key=lambda item:item.freq)
        node_left=queue.pop(0)
        node_right=queue.pop(0)
        node_father=Node(node_left.freq+node_right.freq)
        node_father.left=node_left
        node_father.right=node_right
        node_left.father=node_father
        node_right.father=node_father
        queue.append(node_father)
    queue[0].father=None
    
    return queue[0]

def huffmanEncoding(nodes,root):
    codes=[""]*len(nodes)
    for i in range(len(nodes)):
        node_tmp=nodes[i]
        
        while node_tmp!=root:
            if node_tmp.isLeft():
                codes[i]="0"+codes[i]
            else:
                codes[i]="1"+codes[i]
                
            node_tmp=node_tmp.father
            
    return codes

if __name__=="__main__":
    chars_freqs=[
        ("C",2),("G",2),("E",3),("K",3),("B",4),
        ("F",4),("I",4),("J",4),("D",5),("H",6),
        ("N",6),("L",7),("M",9),("A",10)

    ]
    
    nodes=createNodes([item[1] for item in chars_freqs])
    root=createHuffmanTree(nodes)
    codes=huffmanEncoding(nodes,root)
    
    for item in zip(chars_freqs,codes):
        print("Character:%s freq:%-2d Encoding:%s"%(item[0][0],item[0][1],item[1]))

Character:C freq:2  Encoding:10100
Character:G freq:2  Encoding:10101
Character:E freq:3  Encoding:0000
Character:K freq:3  Encoding:0001
Character:B freq:4  Encoding:0100
Character:F freq:4  Encoding:0101
Character:I freq:4  Encoding:0110
Character:J freq:4  Encoding:0111
Character:D freq:5  Encoding:1011
Character:H freq:6  Encoding:1110
Character:N freq:6  Encoding:1111
Character:L freq:7  Encoding:001
Character:M freq:9  Encoding:100
Character:A freq:10 Encoding:110