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.
public class Solution {
public int numDistinct(String S, String T) {
//special case
int slen = S.length(), tlen = T.length();
if(slen == 0 || tlen == 0 || slen < tlen)
return 0;
//dynamic programming
int[][] num = new int[slen + 1][tlen + 1];
for(int i = 0; i < slen + 1; ++i)
num[i][0] = 1; //take nothing from target string T.
for(int i = 1; i < tlen + 1; ++i)
num[0][i] = 0; //take nothing from source string S.
for(int i = 1; i < slen + 1; ++i) {
for(int j = 1; j < tlen + 1; ++j) {
if(S.charAt(i - 1) == T.charAt(j - 1))
num[i][j] = num[i - 1][j - 1] + num[i - 1][j];
else
num[i][j] = num[i - 1][j];
}
}
return num[slen][tlen];
}
}
leetcode--Distinct Subsequences,布布扣,bubuko.com
leetcode--Distinct Subsequences
原文：http://www.cnblogs.com/averillzheng/p/3825384.html