[动态规划] leetcode 115 Distinct Subsequences

problem:https://leetcode.com/problems/distinct-subsequences/

        字符匹配类型题目。

class Solution {
public:
    vector<vector<int>> dp;
    int numDistinct(string& s, string& t, int i, int j) {
        if(j == t.size()) return 1;
        if(i == s.size()) return 0;
        if(dp[i][j] != -1) return dp[i][j];
        if(s[i] == t[j])
        {
            return dp[i][j] = numDistinct(s, t, i + 1, j + 1) + numDistinct(s, t, i + 1, j);
        }
        else
        {
            return dp[i][j] = numDistinct(s, t, i + 1, j);
        }
    }
    int numDistinct(string s, string t) {
        dp.resize(s.size(), vector<int>(t.size(), -1));
        return numDistinct(s, t, 0, 0);
    }
};