LeetCode "Distinct Subsequences" - TO BE REVISED

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A classic and representative DP problem. To be revised later. Quite a few interesting details to think about.

class Solution {public:    int numDistinct(string S, string T) {        int lenS = S.length();        int lenT = T.length();        if (lenS < lenT) return 0;        if (lenS == lenT)        {            if (S.compare(T) == 0) return 1;            else return 0;        }        vector<int> dp(lenT + 1, 0);        dp[0] = 1;　　　　　　　　　　　　// Point 1        //    S: i, T: j        //    if S[i-1] == T[j - 1]        //        dp[i][j] = dp[i - 1][j] + dp[i - 1][j - 1]        //    else        //        dp[i][j] = dp[i - 1][j]        for (int i = 1; i <= lenS; i ++)        for (int j = lenT; j >= 1; j--) // Point 2        {            if(i < j) continue;            if (S[i - 1] == T[j - 1])                dp[j] += dp[j - 1];　　// Point 3        }        return dp[lenT];    }};