最长公共子序列python实现

def lcs(a,b):
	lena=len(a)
	lenb=len(b)
	c=[[0 for i in range(lenb+1)] for j in range(lena+1)]
	flag=[[0 for i in range(lenb+1)] for j in range(lena+1)]
	for i in range(lena):
		for j in range(lenb):
			if a[i]==b[j]:
				c[i+1][j+1]=c[i][j]+1
				flag[i+1][j+1]=‘ok‘
			elif c[i+1][j]>c[i][j+1]:
				c[i+1][j+1]=c[i+1][j]
				flag[i+1][j+1]=‘left‘
			else:
				c[i+1][j+1]=c[i][j+1]
				flag[i+1][j+1]=‘up‘
	return c,flag

def printLcs(flag,a,i,j):
	if i==0 or j==0:
		return
	if flag[i][j]==‘ok‘:
		printLcs(flag,a,i-1,j-1)
		print(a[i-1],end=‘‘)
	elif flag[i][j]==‘left‘:
		printLcs(flag,a,i,j-1)
	else:
		printLcs(flag,a,i-1,j)
		
a=‘ABCBDAB‘
b=‘BDCABA‘
c,flag=lcs(a,b)
for i in c:
	print(i)
print(‘‘)
for j in flag:
	print(j)
print(‘‘)
printLcs(flag,a,len(a),len(b))
print(‘‘)

4.根据计算最优值得到的信息，构造最优解