算法

每日leetcode-115

Given a string S and a string T, count the number of distinct subsequences of S which equals T.

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).

一个简单的动态规划即可。

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class Solution {
public:
    int numDistinct(string s, string t) {
        int lens = s.size(), lent = t.size();
        vector<vector<int>> dp(lens + 1, vector<int>(lent + 1, 0));
        for (int i = 0; i <= lens; i++) {
            dp[i][0] = 1;
        }
        for (int i = 1; i <= lens; i++) {
            for (int j = 1; j <= i && j <= lent; j++) {
                dp[i][j] = (int)((long long)(s[i - 1] == t[j - 1] ? dp[i - 1][j - 1] : 0) + dp[i - 1][j]);
            }
        }
        return dp[lens][lent];
    }
};