字符串相似性算法【最长公共字符串算法】 【LCS】

#!/user/bin/env python  
# -*- coding: utf-8 -*-  
  
class arithmetic():  
      
    def __init__(self):  
        pass  
    ''' 【编辑距离算法】 【levenshtein distance】 【字符串相似度算法】 '''
    
    def levenshtein(self,first,second):  
        if len(first) > len(second):  
            first,second = second,first  
        if len(first) == 0:  
            return len(second)  
        if len(second) == 0:  
            return len(first)  
        first_length = len(first) + 1  
        second_length = len(second) + 1  
        distance_matrix = [range(second_length) for x in range(first_length)]   
        #print distance_matrix  
        for i in range(1,first_length):  
            for j in range(1,second_length):  
                deletion = distance_matrix[i-1][j] + 1  
                insertion = distance_matrix[i][j-1] + 1  
                substitution = distance_matrix[i-1][j-1]  
                if first[i-1] != second[j-1]:  
                    substitution += 1  
                distance_matrix[i][j] = min(insertion,deletion,substitution)  
        #print distance_matrix  
        return distance_matrix[first_length-1][second_length-1]
    
    def lcs(self,first,second):  
        first_length = len(first)  
        second_length = len(second)  
        size = 0  
        x = 0  
        y = 0  
        matrix = [range(second_length) for x in range(first_length)]  
        #print matrix  
        for i in range(first_length):  
            for j in range(second_length):  
                #print i,j  
                if first[i] == second[j]:  
                    if i - 1 >= 0 and j - 1 >=0:  
                        matrix[i][j] = matrix[i-1][j-1] + 1  
                    else:  
                        matrix[i][j] = 1  
                    if matrix[i][j] > size:  
                        size = matrix[i][j]  
                        x = j  
                        y = i  
                else:  
                    matrix[i][j] = 0  
        #print matrix  
        #print size,x,y   
  
        return second[x-size+1:x+1]  
      
if __name__ == "__main__":  
    arith = arithmetic()  
    print arith.levenshtein('GUMBOsdafsadfdsafsafsadfasfadsfasdfasdfs','GAMBOL00000000000dfasfasfdafsafasfasdfdsa')  
    print arith.lcs('GUMBOsdafsadfdsafsafsadfasfadsfasdfasdfs','GAMBOL00000000000dfasfasfdafsafasfasdfdsa')

 

from：http://www.lamprisi.com/forum.php?mod=viewthread&tid=3935&highlight=LCS