Distinct Subsequences
Given a string S and a string T, count the number of distinct subsequences of T in S.
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).
Here is an example:
S = "rabbbit", T = "rabbit"
Return 3.
Solution
class Solution(object):
def numDistinct(self, s, t):
"""
:type s: str
:type t: str
:rtype: int
"""
m, n = len(s) + 1, len(t) + 1
dp = [[0 for _ in range(n)] for _ in range(m)]
for i in range(m):
dp[i][0] = 1
for i in range(1,m):
for j in range(1,n):
if s[i-1] == t[j-1]:
dp[i][j] = dp[i-1][j] + dp[i-1][j-1]
else:
dp[i][j] = dp[i-1][j]
return dp[m-1][n-1]