LeetCode 115 Distinct Subsequences - Implementation

Count matching subsequences with 2D DP.

def numDistinct(s, t): m, n = len(s), len(t) dp = [[0] * (n + 1) for _ in range(m + 1)]

for i in range(m + 1):
    dp[i][0] = 1

for i in range(1, m + 1):
    for j in range(1, n + 1):
        if s[i - 1] == t[j - 1]:
            dp[i][j] = dp[i - 1][j - 1] + dp[i - 1][j]
        else:
            dp[i][j] = dp[i - 1][j]

return dp[m][n]

$O(m \times n)$ time and space.