115. Distinct Subsequences (Hard) - TengnanYao/daily_leetcode GitHub Wiki

class Solution:
    def numDistinct(self, s: str, t: str) -> int:
        m, n = len(s), len(t)
        dp = [[0] * (m + 1) for _ in range(n + 1)]
        for i in range(m + 1):
            dp[0][i] = 1
        for i in range(n):
            for j in range(i, m):
                if s[j] == t[i]:
                    dp[i + 1][j + 1] = dp[i][j] + dp[i + 1][j]
                else:
                    dp[i + 1][j + 1] = dp[i + 1][j]
        return dp[-1][-1]