[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.

[Solution].java

public class Solution {
    public int numDistinct(String S, String T) {
        // Start typing your Java solution below
        // DO NOT write main() function
        int[][] dp = new int[T.length() + 1][S.length() + 1];
        for(int i = 0; i < dp[0].length; i++) dp[0][i] = 1;
        for(int i = 1; i < dp.length; i++) dp[i][0] = 0;
        for(int i = 1; i < dp.length; i++){
            for(int j = 1; j < dp[0].length; j++){
                dp[i][j] = dp[i][j - 1];
                if(T.charAt(i - 1) == S.charAt(j - 1))
                    dp[i][j] += dp[i - 1][j - 1];
            }
        }
        return dp[T.length()][S.length()];
    }
}