LeetCode 115:Distinct Sequence

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.

这类动态规划题目就是初始化+状态转移式。要多加练习。

public class Solution {
    public int numDistinct(String s, String t) {
        int m=s.length();
        int n=t.length();
        int dp[][]=new int[m+1][n+1];
        dp[0][0]=1;
        for(int i=1;i<m;i++){
            dp[i][0]=1;
        }
        for(int j=1;j<n;j++){
            dp[0][j]=0;
        }
        for(int i=1;i<=m;i++)
        for(int j=1;j<=n;j++){
            if(s.charAt(i-1)==t.charAt(j-1))
            dp[i][j]=dp[i-1][j]+dp[i-1][j-1];
            else
            dp[i][j]=dp[i-1][j];
        }
        return dp[m][n];
        
    }
}