Leetcode: Distinct Subsequences @Python

class Solution:
    # @return an integer
    def numDistinct(self, S, T):
        s=len(S)
        t=len(T)
        dp=[[0 for j in range(s+1)] for i in range(t+1)]
        for j in range(s+1):
            dp[0][j]=1
        for j in range(1,s+1):
            for i in range(1,min(j+1,t+1)):
                if T[i-1]!=S[j-1]:
                    dp[i][j]=dp[i][j-1]
                else:
                    dp[i][j]=dp[i-1][j-1]+dp[i][j-1]
        return dp[t][s]