{"id":9939,"date":"2023-02-12T08:28:04","date_gmt":"2023-02-12T16:28:04","guid":{"rendered":"https:\/\/zxi.mytechroad.com\/blog\/?p=9939"},"modified":"2023-02-12T08:32:01","modified_gmt":"2023-02-12T16:32:01","slug":"leetcode-2563-count-the-number-of-fair-pairs","status":"publish","type":"post","link":"https:\/\/zxi.mytechroad.com\/blog\/two-pointers\/leetcode-2563-count-the-number-of-fair-pairs\/","title":{"rendered":"\u82b1\u82b1\u9171 LeetCode 2563.\u00a0Count the Number of Fair Pairs"},"content":{"rendered":"\n<p>Given a&nbsp;<strong>0-indexed<\/strong>&nbsp;integer array&nbsp;<code>nums<\/code>&nbsp;of size&nbsp;<code>n<\/code>&nbsp;and two integers&nbsp;<code>lower<\/code>&nbsp;and&nbsp;<code>upper<\/code>, return&nbsp;<em>the number of fair pairs<\/em>.<\/p>\n\n\n\n<p>A pair&nbsp;<code>(i, j)<\/code>&nbsp;is&nbsp;<strong>fair&nbsp;<\/strong>if:<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li><code>0 &lt;= i &lt; j &lt; n<\/code>, and<\/li><li><code>lower &lt;= nums[i] + nums[j] &lt;= upper<\/code><\/li><\/ul>\n\n\n\n<p><strong>Example 1:<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-preformatted;crayon:false\"><strong>Input:<\/strong> nums = [0,1,7,4,4,5], lower = 3, upper = 6\n<strong>Output:<\/strong> 6\n<strong>Explanation:<\/strong> There are 6 fair pairs: (0,3), (0,4), (0,5), (1,3), (1,4), and (1,5).\n<\/pre>\n\n\n\n<p><strong>Example 2:<\/strong><\/p>\n\n\n\n<pre class=\"wp-block-preformatted;crayon:false\"><strong>Input:<\/strong> nums = [1,7,9,2,5], lower = 11, upper = 11\n<strong>Output:<\/strong> 1\n<strong>Explanation:<\/strong> There is a single fair pair: (2,3).\n<\/pre>\n\n\n\n<p><strong>Constraints:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\"><li><code>1 &lt;= nums.length &lt;= 10<sup>5<\/sup><\/code><\/li><li><code>nums.length == n<\/code><\/li><li><code>-10<sup>9<\/sup>&nbsp;&lt;= nums[i] &lt;= 10<sup>9<\/sup><\/code><\/li><li><code>-10<sup>9<\/sup>&nbsp;&lt;= lower &lt;= upper &lt;= 10<sup>9<\/sup><\/code><\/li><\/ul>\n\n\n\n<h2 class=\"wp-block-heading\"><strong>Solution: Two Pointers<\/strong><\/h2>\n\n\n\n<p>Sort the array, use two pointers to find how # of pairs (i, j) s.t. nums[i] + nums[j] &lt;= limit.<br>Ans = count(upper) &#8211; count(lower &#8211; 1)<\/p>\n\n\n\n<p>Time complexity: O(n)<br>Space complexity: O(1)<\/p>\n\n\n\n<div class=\"responsive-tabs\">\n<h2 class=\"tabtitle\">C++<\/h2>\n<div class=\"tabcontent\">\n\n<pre lang=\"c++\">\n\/\/ Author: Huahua\nclass Solution {\npublic:\n  long long countFairPairs(vector<int>& nums, int lower, int upper) {\n    sort(begin(nums), end(nums));\n    auto count = [&](int limit) -> long long {\n      long long ans = 0;\n      for (int i = 0, j = nums.size() - 1; i < j; ++i) {\n        while (i < j &#038;&#038; nums[i] + nums[j] > limit) --j;\n        ans += j - i;\n      }\n      return ans;\n    };\n    return count(upper) - count(lower - 1);\n  }\n};\n<\/pre>\n<\/div><\/div>\n","protected":false},"excerpt":{"rendered":"<p>Given a&nbsp;0-indexed&nbsp;integer array&nbsp;nums&nbsp;of size&nbsp;n&nbsp;and two integers&nbsp;lower&nbsp;and&nbsp;upper, return&nbsp;the number of fair pairs. A pair&nbsp;(i, j)&nbsp;is&nbsp;fair&nbsp;if: 0 &lt;= i &lt; j &lt; n, and lower &lt;= nums[i]&#8230;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[176],"tags":[20,177,148,175],"class_list":["post-9939","post","type-post","status-publish","format-standard","hentry","category-two-pointers","tag-array","tag-medium","tag-pair","tag-two-pointers","entry","simple"],"_links":{"self":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts\/9939","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/comments?post=9939"}],"version-history":[{"count":2,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts\/9939\/revisions"}],"predecessor-version":[{"id":9941,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/posts\/9939\/revisions\/9941"}],"wp:attachment":[{"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/media?parent=9939"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/categories?post=9939"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/zxi.mytechroad.com\/blog\/wp-json\/wp\/v2\/tags?post=9939"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}