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