Given a string S, count the number of distinct, non-empty subsequences of S . Since the result may be large, return the answer modulo 10^9 + 7. Example 1: Input: "abc" Output: 7 Explanation: The 7 distinct subsequences are "a", "b", "c", "ab", "ac", "bc", and "abc". Example 2: Input: "aba" Output: 6 Explanation: The 6 distinct subsequences are "a", "b", "ab", "ba", "aa" and "aba". Example 3: Input: "aaa" Output: 3 Explanation: The 3 distinct subsequences are "a", "aa" and "aaa". Note: S contains only lowercase letters. 1 <= S.length <= 2000