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
.
思考:DP。
class Solution { public: int numDistinct(string S, string T) { int slen = S.size(); int tlen = T.size(); vector<vector<int> > dp(tlen + 1, vector<int>(slen + 1, 0)); for(int i = 0; i <= slen; ++i) dp[0][i] = 1; for(int i = 1; i <= tlen; ++i) { for(int j = 1; j <= slen; ++j) { if(S[j - 1] == T[i - 1]) { dp[i][j] = dp[i][j - 1] + dp[i - 1][j - 1]; } else { dp[i][j] = dp[i][j - 1]; } } } return dp[tlen][slen]; } };