【LeetCode】Distinct Subsequences
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参考链接
http://blog.csdn.net/xshalk/article/details/8223120
http://blog.csdn.net/bigapplestar/article/details/17523391
http://blog.csdn.net/jellyyin/article/details/9060709
题目描述
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
.
题目分析
题意:
给定2个字符串a, b,求b在a中出现的次数。要求可以是不连续的,但是b在a中的顺序必须和b以前的一致。
示例说明:思路:动态规划的关键就是找递归公式。
类似于数字分解的题目。dp[i][j]表示:b的前j个字符在a的前i个字符中出现的次数。
如果a[i] == b[j]则 dp[i][j] = dp[i-1][j] + dp[i-1][j-1]
如果a[i] != b[j]则 dp[i][j] = dp[i-1][j]
总结
这个一个典型的动态规划题,需要多多复习。代码示例
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