lc 115. Distinct Subsequences

https://leetcode.com/problems/distinct-subsequences/description/

求串s中有几个字串t？

开始看成了s和t有几个公共字串，想来也是dp。题目中明显s和t不是对称的。

对于s中最后字符c，如果和t中最后一个不同，那么去掉这个c是对结果无影响的。

如果相同，我们有两种选择：用它，不用它。

于是就是：

if s[i]==t[j]:    dp[i][j]=dp[i-1][j-1]+dp[i-1][j]else:    dp[i][j] = dp[i - 1][j]

code：

class Solution:def update(self,i,j):if i<0 or j<0:return 0def numDistinct(self, s, t):""":type s: str:type t: str:rtype: int"""sl=len(s)tl=len(t)if sl*tl==0:return 0dp=[[0]*tl for _ in range(sl)]if s[0]==t[0]:dp[0][0]=1for i in range(1,sl):dp[i][0]=dp[i-1][0]if s[i]==t[0]:dp[i][0]+=1for i in range(1,sl):for j in range(1,tl):if s[i]==t[j]:dp[i][j]=dp[i-1][j-1]+dp[i-1][j]else:dp[i][j] = dp[i - 1][j]# print(dp)return dp[-1][-1]
s=Solution()
print(s.numDistinct("babgbag", "bag"))
# print(s.numDistinct("rabbbit", "rabbit"))

转载于:https://www.cnblogs.com/waldenlake/p/9678522.html

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