题目1： 115. 不同的子序列
代码：

class Solution {
public:
    int numDistinct(string s, string t) {
    int m = s.size();
    int n = t.size();
        vector<vector<uint64_t>> dp(m + 1, vector<uint64_t>(n+ 1));
        for (int i = 0; i < m; i++) dp[i][0] = 1;

        for (int i = 1; i <= m; i++) {
            for (int j = 1; j <= n; j++) {
                if (s[i - 1] == t[j - 1]) {
                    dp[i][j] = dp[i - 1][j - 1] + dp[i - 1][j];
                } else {
                    dp[i][j] = dp[i - 1][j];
                }
            }
        }
        return dp[m][n];
    }
};

题目2： 583. 两个字符串的删除操作

代码：

class Solution {
public:
    int minDistance(string word1, string word2) {
        int m = word1.length();
        int n = word2.length();
        vector<vector<int>> dp(m + 1, vector<int>(n + 1));

        for(int i = 0; i <= m; i++) dp[i][0] = i;
        for(int j = 0; j <= n; j++) dp[0][j] = j;

        for(int i = 1; i <= m; i++) {
            for(int j = 1; j <= n; j++) {
                if(word1[i - 1] == word2[j - 1]) dp[i][j] = dp[i - 1][j - 1];
                else dp[i][j] = min(dp[i - 1][j], dp[i][j - 1]) + 1;
            }
        } 
        return dp[m][n];
    }
};

题目3： 72. 编辑距离
代码:

class Solution {
public:
    int minDistance(string word1, string word2) {
        int m = word1.length();
        int n = word2.length();

        vector<vector<int>> dp(m + 1, vector<int>(n + 1));

        for(int i = 0; i <= m; i++) dp[i][0] = i;
        for(int j = 0; j <= n; j++) dp[0][j] = j;

        for(int i = 1; i <= m; i++) {
            for(int j = 1; j <= n; j++) {
                if(word1[i - 1] == word2[j - 1])  {dp[i][j] = dp[i - 1][j - 1];}
                else  {dp[i][j] = min(dp[i - 1][j - 1], min(dp[i - 1][j], dp[i][j - 1])) + 1;}
            }
        }
        return dp[m][n];
    }
};