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"title": "Count Pairs With XOR in a Range",
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"content": "<p>Given a <strong>(0-indexed)</strong> integer array <code>nums</code> and two integers <code>low</code> and <code>high</code>, return <em>the number of <strong>nice pairs</strong></em>.</p>\r\n\r\n<p>A <strong>nice pair</strong> is a pair <code>(i, j)</code> where <code>0 <= i < j < nums.length</code> and <code>low <= (nums[i] XOR nums[j]) <= high</code>.</p>\r\n\r\n<p> </p>\r\n<p><strong>Example 1:</strong></p>\r\n\r\n<pre>\r\n<strong>Input:</strong> nums = [1,4,2,7], low = 2, high = 6\r\n<strong>Output:</strong> 6\r\n<strong>Explanation:</strong> All nice pairs (i, j) are as follows:\r\n - (0, 1): nums[0] XOR nums[1] = 5 \r\n - (0, 2): nums[0] XOR nums[2] = 3\r\n - (0, 3): nums[0] XOR nums[3] = 6\r\n - (1, 2): nums[1] XOR nums[2] = 6\r\n - (1, 3): nums[1] XOR nums[3] = 3\r\n - (2, 3): nums[2] XOR nums[3] = 5\r\n</pre>\r\n\r\n<p><strong>Example 2:</strong></p>\r\n\r\n<pre>\r\n<strong>Input:</strong> nums = [9,8,4,2,1], low = 5, high = 14\r\n<strong>Output:</strong> 8\r\n<strong>Explanation:</strong> All nice pairs (i, j) are as follows:\r\n - (0, 2): nums[0] XOR nums[2] = 13\r\n - (0, 3): nums[0] XOR nums[3] = 11\r\n - (0, 4): nums[0] XOR nums[4] = 8\r\n - (1, 2): nums[1] XOR nums[2] = 12\r\n - (1, 3): nums[1] XOR nums[3] = 10\r\n - (1, 4): nums[1] XOR nums[4] = 9\r\n - (2, 3): nums[2] XOR nums[3] = 6\r\n - (2, 4): nums[2] XOR nums[4] = 5</pre>\r\n\r\n<p> </p>\r\n<p><strong>Constraints:</strong></p>\r\n\r\n<ul>\r\n\t<li><code>1 <= nums.length <= 2 * 10<sup>4</sup></code></li>\r\n\t<li><code>1 <= nums[i] <= 2 * 10<sup>4</sup></code></li>\r\n\t<li><code>1 <= low <= high <= 2 * 10<sup>4</sup></code></li>\r\n</ul>",
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"code": "class Solution {\npublic:\n int countPairs(vector<int>& nums, int low, int high) {\n \n }\n};",
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"code": "class Solution(object):\n def countPairs(self, nums, low, high):\n \"\"\"\n :type nums: List[int]\n :type low: int\n :type high: int\n :rtype: int\n \"\"\"\n ",
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"code": "/**\n * @param {number[]} nums\n * @param {number} low\n * @param {number} high\n * @return {number}\n */\nvar countPairs = function(nums, low, high) {\n \n};",
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"code": "# @param {Integer[]} nums\n# @param {Integer} low\n# @param {Integer} high\n# @return {Integer}\ndef count_pairs(nums, low, high)\n \nend",
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"hints": [
"Let's note that we can count all pairs with XOR ≤ K, so the answer would be to subtract the number of pairs withs XOR < low from the number of pairs with XOR ≤ high.",
"For each value, find out the number of values when you XOR it with the result is ≤ K using a trie."
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