77. Longest Common Subsequence

class Solution:
    def longestCommonSubsequence(self, A, B):
        # init
        n1, n2 = len(A), len(B)
        f = [[0] * (n2 + 1) for _ in range(n1 + 1)]
        for i in range(1, n1 + 1):
            for j in range(1, n2 + 1):
                f[i][j] = max(f[i - 1][j], f[i][j - 1])
                if A[i - 1] == B[j - 1]:
                    f[i][j] = max(f[i][j], f[i - 1][j - 1] + 1)
        return f[n1][n2]