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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).
Example
Given S = "rabbbit", T = "rabbit", return 3.
Do it in O(n2) time and O(n) memory.
O(n2) memory is also acceptable if you do not know how to optimize memory.
public class Solution { /** * @param S, T: Two string. * @return: Count the number of distinct subsequences */ public int numDistinct(String S, String T) { // write your code here if(T.length()==0) return 1; if(S.length()==0) return 0; int m=S.length(); int n=T.length(); int[][] res=new int[m+1][n+1]; for(int i=0;i<=m;i++) { res[i][0]=1; } for(int i=1;i<=m;i++) { for(int j=1;j<=n;j++) { if(S.charAt(i-1)==T.charAt(j-1)) { res[i][j]=res[i-1][j-1]+res[i-1][j]; } else { res[i][j]=res[i-1][j]; } } } return res[m][n]; } }
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原文地址：http://www.cnblogs.com/kittyamin/p/5115368.html
