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 Summary

Constructors

Constructor and Description
Solution()

Method Summary

Modifier and Type	Method and Description
int	numPermsDISequence(String s)

Methods inherited from class java.lang.Object

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

Constructor Detail

Solution

public Solution()

Method Detail

numPermsDISequence

public int numPermsDISequence(String s)