Package g0901_1000.s0903_valid_permutations_for_di_sequence

Class Solution

java.lang.Object
g0901_1000.s0903_valid_permutations_for_di_sequence.Solution
public class Solution extends Object
903 - Valid Permutations for DI Sequence.

Hard

You are given a string s of length n where s[i] is either:

  • 'D' means decreasing, or
  • 'I' means increasing.

A permutation perm of n + 1 integers of all the integers in the range [0, n] is called a valid permutation if for all valid i:

  • If s[i] == 'D', then perm[i] > perm[i + 1], and
  • If s[i] == 'I', then perm[i] < perm[i + 1].

Return the number of valid permutations perm. Since the answer may be large, return it modulo 109 + 7.

Example 1:

Input: s = “DID”

Output: 5

Explanation: The 5 valid permutations of (0, 1, 2, 3) are: (1, 0, 3, 2) (2, 0, 3, 1) (2, 1, 3, 0) (3, 0, 2, 1) (3, 1, 2, 0)

Example 2:

Input: s = “D”

Output: 1

Constraints:

  • n == s.length
  • 1 <= n <= 200
  • s[i] is either 'I' or 'D'.

  • Constructor Details

    • Solution

      public Solution()

  • Method Details

    • numPermsDISequence

      public int numPermsDISequence(String s)