Package g1801_1900.s1866_number_of_ways_to_rearrange_sticks_with_k_sticks_visible

Class Solution

java.lang.Object
g1801_1900.s1866_number_of_ways_to_rearrange_sticks_with_k_sticks_visible.Solution
public class Solution extends java.lang.Object
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 109 + 7.

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 109 + 7) ways to rearrange the sticks such that exactly 11 sticks are visible.

Constraints:

  • 1 <= n <= 1000
  • 1 <= k <= n

  • Constructor Summary

    Constructors
    Constructor
    Description
    Solution()
     

  • Method Summary

    Modifier and Type
    Method
    Description
    int
    rearrangeSticks(int n, int k)
     

    Methods inherited from class java.lang.Object

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

  • Constructor Details

    • Solution

      public Solution()

  • Method Details

    • rearrangeSticks

      public int rearrangeSticks(int n, int k)