动态规划两个数组dp问题系列一＞不同的子序列

class Solution {
    public int numDistinct(String s, String t) {
        int m = t.length(), n = s.length();
        int[][] dp = new int[m+1][n+1];

        //初始化
        for(int i = 0; i <= n; i++) dp[0][i] = 1;

        for(int i = 1; i <= m; i++)
            for(int j = 1; j <= n; 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[m][n];    
    }
}