Distinct Subsequences
问题：
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.
思路：
动态规划
我的代码：
public class Solution { public int numDistinct(String S, String T) { if(S == null || S.length() == 0 || T == null || T.length() == 0) return 0; int cols = S.length(); int rows = T.length(); if(rows > cols) return 0; int[][] dp = new int[rows+1][cols+1]; for(int j = 0; j <= cols; j++) { dp[0][j] = 1; } for(int i = 1; i <= rows; i++) { for(int j = 1; j <= cols; j++) { dp[i][j] = dp[i][j-1]; if(S.charAt(j-1) == T.charAt(i-1)) { dp[i][j] += dp[i-1][j-1]; } } } return dp[rows][cols]; } }
学习之处：
原文：http://www.cnblogs.com/sunshisonghit/p/4374838.html
