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leetcode--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.
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]; }}
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