115 Distinct Subsequences

115 Distinct Subsequences

这道题是dp, 我定义的dp[i][j] 为用t[:i] 和s[:j] 的disitinct subsequence排列数

class Solution:
    # @param {string} s
    # @param {string} t
    # @return {integer}
    def numDistinct(self, s, t):
        m, n = len(t), len(s)
        if m == 0 or n == 0:
            return 0
        dp,cur = [0] * n, 1
        for i in range(0, m):
            for j in range(0, n):
                tmp = dp[j]
                if t[i] == s[j]:
                    dp[j] = cur
                else:
                    dp[j] = 0
                cur += tmp
            cur = 0
        return sum(dp)