Find Length of Longest Common Subsequences for Large String

Dynamic Program used to find length of longest common subsequences (adopted from http://www.geeksforgeeks.org/dynamic-programming-set-4-longest-common-subsequence/)

def lcs(X, Y):
    # find the length of the strings

    m = len(X)
    n = len(Y)
    previous = [0] * (len(Y)+1)
    current = [0] * (len(Y)+1)

    for i in xrange(m + 1):
        for j in xrange(n + 1):
            if i == 0 or j == 0:
                current[j] = 0   

            elif X[i - 1] == Y[j - 1]:
                current[j] = previous[j - 1] + 1

            else:
                current[j] = max(previous[j], current[j - 1])
        previous = current
        current = [0] * (len(Y)+1)
    return previous[n]


X = "AGGTAB"Y = "GXTXAYB"print "Length of LCS is ", lcs(X,Y)