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.<p>Hard</p> <p>You are given a string <code>s</code> of length <code>n</code> where <code>s[i]</code> is either:</p> <ul> <li><code>'D'</code> means decreasing, or</li> <li><code>'I'</code> means increasing.</li> </ul> <p>A permutation <code>perm</code> of <code>n + 1</code> integers of all the integers in the range <code>[0, n]</code> is called a <strong>valid permutation</strong> if for all valid <code>i</code>:</p> <ul> <li>If <code>s[i] == 'D'</code>, then <code>perm[i] > perm[i + 1]</code>, and</li> <li>If <code>s[i] == 'I'</code>, then <code>perm[i] < perm[i + 1]</code>.</li> </ul> <p>Return <em>the number of <strong>valid permutations</strong></em> <code>perm</code>. Since the answer may be large, return it <strong>modulo</strong> <code>10⁹ + 7</code>.</p> <p><strong>Example 1:</strong></p> <p><strong>Input:</strong> s = &ldquo;DID&rdquo;</p> <p><strong>Output:</strong> 5</p> <p><strong>Explanation:</strong> 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)</p> <p><strong>Example 2:</strong></p> <p><strong>Input:</strong> s = &ldquo;D&rdquo;</p> <p><strong>Output:</strong> 1</p> <p><strong>Constraints:</strong></p> <ul> <li><code>n == s.length</code></li> <li><code>1 <= n <= 200</code></li> <li><code>s[i]</code> is either <code>'I'</code> or <code>'D'</code>.</li> </ul>

Constructor Summary

Constructors

Constructor	Description
Solution()

Method Summary

Modifier and Type	Method	Description
int	numPermsDISequence(String s)

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

numPermsDISequence

public int numPermsDISequence(String s)