Package g1601_1700.s1639_number_of_ways_to_form_a_target_string_given_a_dictionary

Class Solution

  • All Implemented Interfaces:
    
public final class Solution

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

    Hard

    You are given a list of strings of the same length words and a string target.

    Your task is to form target using the given words under the following rules:

    • target should be formed from left to right.

    • To form the <code>i<sup>th</sup></code> character ( 0-indexed ) of target, you can choose the <code>k<sup>th</sup></code> character of the <code>j<sup>th</sup></code> string in words if target[i] = words[j][k].

    • Once you use the <code>k<sup>th</sup></code> character of the <code>j<sup>th</sup></code> string of words, you can no longer use the <code>x<sup>th</sup></code> character of any string in words where x &lt;= k. In other words, all characters to the left of or at index k become unusuable for every string.

    • Repeat the process until you form the string target.

    Notice that you can use multiple characters from the same string in words provided the conditions above are met.

    Return the number of ways to form target from words. Since the answer may be too large, return it modulo <code>10<sup>9</sup> + 7</code>.

    Example 1:

    Input: words = "acca","bbbb","caca", target = "aba"

    Output: 6

    Explanation: There are 6 ways to form target.

    "aba" -> index 0 ("acca"), index 1 ("bbbb"), index 3 ("caca")

    "aba" -> index 0 ("acca"), index 2 ("bbbb"), index 3 ("caca")

    "aba" -> index 0 ("acca"), index 1 ("bbbb"), index 3 ("acca")

    "aba" -> index 0 ("acca"), index 2 ("bbbb"), index 3 ("acca")

    "aba" -> index 1 ("caca"), index 2 ("bbbb"), index 3 ("acca")

    "aba" -> index 1 ("caca"), index 2 ("bbbb"), index 3 ("caca")

    Example 2:

    Input: words = "abba","baab", target = "bab"

    Output: 4

    Explanation: There are 4 ways to form target.

    "bab" -> index 0 ("baab"), index 1 ("baab"), index 2 ("abba")

    "bab" -> index 0 ("baab"), index 1 ("baab"), index 3 ("baab")

    "bab" -> index 0 ("baab"), index 2 ("baab"), index 3 ("baab")

    "bab" -> index 1 ("abba"), index 2 ("baab"), index 3 ("baab")

    Constraints:

    • 1 &lt;= words.length &lt;= 1000

    • 1 &lt;= words[i].length &lt;= 1000

    • All strings in words have the same length.

    • 1 &lt;= target.length &lt;= 1000

    • words[i] and target contain only lowercase English letters.

    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description

    • Field Summary

      Fields 
      Modifier and Type Field Description

    • Constructor Summary

      Constructors 
      Constructor Description
      Solution()

    • Enum Constant Summary

      Enum Constants 
      Enum Constant Description

    • Method Summary

      Modifier and Type Method Description
      final Integer numWays(Array<String> words, String target)

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait