count-nice-pairs-in-an-array

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Algorithms

You are given an array <code>nums</code> that consists of non-negative integers. Let us define <code>rev(x)</code> as the reverse of the non-negative integer <code>x</code>. For example, <code>rev(123) = 321</code>, and <code>rev(120) = 21</code>. A pair of indices <code>(i, j)</code> is nice if it satisfies all of the following conditions:

<ul>
	<li><code>0 &lt;= i &lt; j &lt; nums.length</code></li>
	<li><code>nums[i] + rev(nums[j]) == nums[j] + rev(nums[i])</code></li>
</ul>

Return the number of nice pairs of indices. Since that number can be too large, return it modulo <code>109 + 7</code>.

&nbsp;
Example 1:

<pre>
Input: nums = [42,11,1,97]
Output: 2
Explanation: The two pairs are:
 - (0,3) : 42 + rev(97) = 42 + 79 = 121, 97 + rev(42) = 97 + 24 = 121.
 - (1,2) : 11 + rev(1) = 11 + 1 = 12, 1 + rev(11) = 1 + 11 = 12.
</pre>

Example 2:

<pre>
Input: nums = [13,10,35,24,76]
Output: 4
</pre>

&nbsp;
Constraints:

<ul>
	<li><code>1 &lt;= nums.length &lt;= 105</code></li>
	<li><code>0 &lt;= nums[i] &lt;= 109</code></li>
</ul>

countNicePairs

Count Nice Pairs in an Array

Number of Pairs of Interchangeable Rectangles

number-of-pairs-of-interchangeable-rectangles

可互换矩形的组数

Count Number of Bad Pairs

count-number-of-bad-pairs

统计坏数对的数目

Number of Pairs Satisfying Inequality

number-of-pairs-satisfying-inequality

满足不等式的数对数目

Array

Hash Table

Math

Counting

给你一个数组 <code>nums</code> ，数组中只包含非负整数。定义 <code>rev(x)</code> 的值为将整数 <code>x</code> 各个数字位反转得到的结果。比方说 <code>rev(123) = 321</code> ， <code>rev(120) = 21</code> 。我们称满足下面条件的下标对 <code>(i, j)</code> 是 好的 ：

<ul>
	<li><code>0 &lt;= i &lt; j &lt; nums.length</code></li>
	<li><code>nums[i] + rev(nums[j]) == nums[j] + rev(nums[i])</code></li>
</ul>

请你返回好下标对的数目。由于结果可能会很大，请将结果对 <code>109 + 7</code> 取余 后返回。

 

示例 1：

<pre>输入：nums = [42,11,1,97]
输出：2
解释：两个坐标对为：
 - (0,3)：42 + rev(97) = 42 + 79 = 121, 97 + rev(42) = 97 + 24 = 121 。
 - (1,2)：11 + rev(1) = 11 + 1 = 12, 1 + rev(11) = 1 + 11 = 12 。
</pre>

示例 2：

<pre>输入：nums = [13,10,35,24,76]
输出：4
</pre>

 

提示：

<ul>
	<li><code>1 &lt;= nums.length &lt;= 105</code></li>
	<li><code>0 &lt;= nums[i] &lt;= 109</code></li>
</ul>