Package g1801_1900.s1866_number_of_ways_to_rearrange_sticks_with_k_sticks_visible

Class Solution

  • All Implemented Interfaces:
    
public final class Solution

    1866 - Number of Ways to Rearrange Sticks With K Sticks Visible\.

    Hard

    There are n uniquely-sized sticks whose lengths are integers from 1 to n. You want to arrange the sticks such that exactly k sticks are visible from the left. A stick is visible from the left if there are no longer sticks to the left of it.

    • For example, if the sticks are arranged [1,3,2,5,4], then the sticks with lengths 1, 3, and 5 are visible from the left.

    Given n and k, return the number of such arrangements. Since the answer may be large, return it modulo <code>10<sup>9</sup> + 7</code>.

    Example 1:

    Input: n = 3, k = 2

    Output: 3

    Explanation: 1,3,2, 2,3,1, and 2,1,3 are the only arrangements such that exactly 2 sticks are visible. The visible sticks are underlined.

    Example 2:

    Input: n = 5, k = 5

    Output: 1

    Explanation: 1,2,3,4,5 is the only arrangement such that all 5 sticks are visible. The visible sticks are underlined.

    Example 3:

    Input: n = 20, k = 11

    Output: 647427950

    Explanation: There are 647427950 (mod 10<sup>9</sup> \+ 7) ways to rearrange the sticks such that exactly 11 sticks are visible.

    Constraints:

    • 1 &lt;= n &lt;= 1000

    • 1 &lt;= k &lt;= n

    • 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 rearrangeSticks(Integer n, Integer k)

      • Methods inherited from class java.lang.Object

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