1639 Number of Ways to Form a Target String Given a Dictionary

1639 Number of Ways to Form a Target String Given a Dictionary. This Java code calculates the number of ways to form
a given target string using characters from an array of words.
Explanation:
1. Initialization: It sets a modulus value for large numbers and determines the lengths
of the target string (m) and the words (k).
2. Frequency Count: It creates a 2D frequency array to count how many times each character (from 'a' to 'z')
appears at each position in the provided words.
3. Dynamic Programming (DP) Setup: It initializes a 2D DP array where dp[i][j] represents
the number of ways to form the prefix of the target up to index i using characters from the words starting at index j.
4. Filling the DP Table:
- The first row is initialized based on the frequency of the first character of the target.
- The rest of the DP table is filled by considering previous results and the number of ways to use the current character from the target.
5. Final Result: The method returns the number of ways to form the complete target string using
the characters from the words, modulo 1,000,000,007.
Overall, the code efficiently computes the desired count using frequency analysis and dynamic programming.