Package g2701_2800.s2748_number_of_beautiful_pairs

Class Solution

java.lang.Object
g2701_2800.s2748_number_of_beautiful_pairs.Solution
public class Solution extends Object
2748 - Number of Beautiful Pairs.<p>Easy</p> <p>You are given a <strong>0-indexed</strong> integer array <code>nums</code>. A pair of indices <code>i</code>, <code>j</code> where <code>0 <= i < j < nums.length</code> is called beautiful if the <strong>first digit</strong> of <code>nums[i]</code> and the <strong>last digit</strong> of <code>nums[j]</code> are <strong>coprime</strong>.</p> <p>Return <em>the total number of beautiful pairs in</em> <code>nums</code>.</p> <p>Two integers <code>x</code> and <code>y</code> are <strong>coprime</strong> if there is no integer greater than 1 that divides both of them. In other words, <code>x</code> and <code>y</code> are coprime if <code>gcd(x, y) == 1</code>, where <code>gcd(x, y)</code> is the <strong>greatest common divisor</strong> of <code>x</code> and <code>y</code>.</p> <p><strong>Example 1:</strong></p> <p><strong>Input:</strong> nums = [2,5,1,4]</p> <p><strong>Output:</strong> 5</p> <p><strong>Explanation:</strong> There are 5 beautiful pairs in nums:</p> <p>When i = 0 and j = 1: the first digit of nums[0] is 2, and the last digit of nums[1] is 5. We can confirm that 2 and 5 are coprime, since gcd(2,5) == 1.</p> <p>When i = 0 and j = 2: the first digit of nums[0] is 2, and the last digit of nums[2] is 1. Indeed, gcd(2,1) == 1.</p> <p>When i = 1 and j = 2: the first digit of nums[1] is 5, and the last digit of nums[2] is 1. Indeed, gcd(5,1) == 1.</p> <p>When i = 1 and j = 3: the first digit of nums[1] is 5, and the last digit of nums[3] is 4. Indeed, gcd(5,4) == 1.</p> <p>When i = 2 and j = 3: the first digit of nums[2] is 1, and the last digit of nums[3] is 4. Indeed, gcd(1,4) == 1.</p> <p>Thus, we return 5.</p> <p><strong>Example 2:</strong></p> <p><strong>Input:</strong> nums = [11,21,12]</p> <p><strong>Output:</strong> 2</p> <p><strong>Explanation:</strong> There are 2 beautiful pairs:</p> <p>When i = 0 and j = 1: the first digit of nums[0] is 1, and the last digit of nums[1] is 1. Indeed, gcd(1,1) == 1.</p> <p>When i = 0 and j = 2: the first digit of nums[0] is 1, and the last digit of nums[2] is 2. Indeed, gcd(1,2) == 1.</p> <p>Thus, we return 2.</p> <p><strong>Constraints:</strong></p> <ul> <li><code>2 <= nums.length <= 100</code></li> <li><code>1 <= nums[i] <= 9999</code></li> <li><code>nums[i] % 10 != 0</code></li> </ul>

  • Constructor Details

    • Solution

      public Solution()

  • Method Details

    • countBeautifulPairs

      public int countBeautifulPairs(int[] nums)