Leetcode 115. Distinct Subsequences
Given a string S and a string T, count the number of distinct subsequences of S which equals T.A subsequence of a string is a new string which is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (ie, "ACE" is a subsequence of "ABCDE" while "AEC" is not).
It's guaranteed the answer fits on a 32-bit signed integer.
Example 1:
Input: S = "rabbbit", T = "rabbit"
Output: 3
Explanation:
As shown below, there are 3 ways you can generate "rabbit" from S.
(The caret symbol ^ means the chosen letters)
rabbbit
^^^^ ^^
rabbbit
^^ ^^^^
rabbbit
^^^ ^^^
Example 2:
Input: S = "babgbag", T = "bag"
Output: 5
Explanation:
As shown below, there are 5 ways you can generate "bag" from S.
(The caret symbol ^ means the chosen letters)
babgbag
^^^
babgbag
^^ ^
babgbag
^ ^^
babgbag
^ ^^
babgbag
^^^
class Solution:
def numDistinct(self, s: str, t: str) -> int:
m, n = len(s), len(t)
dp = [ for _ in range(m + 1)]
for i in range(m + 1):
for j in range(n + 1):
if j == 0:
dp = 1
continue
if i == 0:
dp = 0
continue
dp = dp
if s == t:
dp += dp
return dp
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