class Solution {//dp[i][j]表示s中前i个字符包含t中前j个字符的个数public int numDistinct(String s, String t) {int n1 = s.length();int n2 = t.length();if(n1 < n2) return 0;int[][] dp = new int[n1 + 1][n2 + 1];for(int i = 0; i <= n1; i++) dp[i][0] = 1;for(int i = 1; i <= n1; i++){for(int j = 1; j <= n2; j++){if(s.charAt(i - 1) == t.charAt(j - 1)){dp[i][j] = dp[i - 1][j - 1] + dp[i - 1][j];}else{dp[i][j] = dp[i - 1][j];}}}return dp[n1][n2];}
}