最长公共子序列(LCS)问题 python

#!/usr/bin/env python
# -*- coding: utf-8 -*

def lcs(arr1, arr2):  
    m = len(arr1)  
    n = len(arr2)  
    c = [[0 for k in range(n + 1)] for k in range(m + 1)]  
    b = [[-1 for k in range(n)] for k in range(m)]  
    for i in range(1, m + 1):  
        for j in range(1, n + 1):  
            if arr1[i - 1] == arr2[j - 1]:  
                c[i][j] = c[i - 1][j - 1] + 1  
                b[i - 1][j - 1] = '↖'   
            elif c[i - 1][j] >= c[i][j - 1]:  
                c[i][j] = c[i - 1][j]  
                b[i - 1][j - 1] = '↑'   
            else:  
                c[i][j] = c[i][j - 1]  
                b[i - 1][j - 1] = '←'   
    rlcs = []  
    get_lcs_arr(b, arr1, len(arr1) - 1, len(arr2) - 1, rlcs)  
    return c[m][n], rlcs  
  
def get_lcs_arr(b, X, i, j, arr):  
    if i < 0 or j < 0:  
        return  
    if b[i][j] == '↖':  
        get_lcs_arr(b, X, i - 1, j - 1, arr)  
        arr.append(X[i])  
    elif b[i][j] == '↑':  
        get_lcs_arr(b, X, i - 1, j, arr)  
    else:  
        get_lcs_arr(b, X, i, j - 1, arr)