Package g1901_2000.s1922_count_good_numbers

Class Solution

java.lang.Object
g1901_2000.s1922_count_good_numbers.Solution
public class Solution extends Object
1922 - Count Good Numbers.<p>Medium</p> <p>A digit string is <strong>good</strong> if the digits <strong>(0-indexed)</strong> at <strong>even</strong> indices are <strong>even</strong> and the digits at <strong>odd</strong> indices are <strong>prime</strong> (<code>2</code>, <code>3</code>, <code>5</code>, or <code>7</code>).</p> <ul> <li>For example, <code>&quot;2582&quot;</code> is good because the digits (<code>2</code> and <code>8</code>) at even positions are even and the digits (<code>5</code> and <code>2</code>) at odd positions are prime. However, <code>&quot;3245&quot;</code> is <strong>not</strong> good because <code>3</code> is at an even index but is not even.</li> </ul> <p>Given an integer <code>n</code>, return <em>the <strong>total</strong> number of good digit strings of length</em> <code>n</code>. Since the answer may be large, <strong>return it modulo</strong> <code>10<sup>9</sup> + 7</code>.</p> <p>A <strong>digit string</strong> is a string consisting of digits <code>0</code> through <code>9</code> that may contain leading zeros.</p> <p><strong>Example 1:</strong></p> <p><strong>Input:</strong> n = 1</p> <p><strong>Output:</strong> 5</p> <p><strong>Explanation:</strong> The good numbers of length 1 are &ldquo;0&rdquo;, &ldquo;2&rdquo;, &ldquo;4&rdquo;, &ldquo;6&rdquo;, &ldquo;8&rdquo;.</p> <p><strong>Example 2:</strong></p> <p><strong>Input:</strong> n = 4</p> <p><strong>Output:</strong> 400</p> <p><strong>Example 3:</strong></p> <p><strong>Input:</strong> n = 50</p> <p><strong>Output:</strong> 564908303</p> <p><strong>Constraints:</strong></p> <ul> <li><code>1 <= n <= 10<sup>15</sup></code></li> </ul>

  • Constructor Details

    • Solution

      public Solution()

  • Method Details

    • countGoodNumbers

      public int countGoodNumbers(long n)