逆序对 on 111qqz's bloghttps://111qqz.com/en/tags/%E9%80%86%E5%BA%8F%E5%AF%B9/Recent content in 逆序对 on 111qqz's blogHugo -- gohugo.ioen© 2015-2026 111qqzTue, 20 Sep 2016 12:07:02 +0000codeforces 540 E. Infinite Inversions (分类思想+线段树求逆序对)https://111qqz.com/en/post/acm-icpc/2016/2016-09-20-cf540e/Tue, 20 Sep 2016 12:07:02 +0000https://111qqz.com/en/post/acm-icpc/2016/2016-09-20-cf540e/<p><a href="http://codeforces.com/problemset/problem/540/E" target="_blank" rel="noreferrer">题目链接</a></p> <p>题意：一个无穷数列，从1开始，初始第i个位置上为i，给出n个swap，每次交换两个位置的数。问交换n次以后得到的数列中，逆序对的数。</p>codeforces 220 E. Little Elephant and Inversions (树状数组+尺取)https://111qqz.com/en/post/acm-icpc/2016/2016-09-15-cf220e/Thu, 15 Sep 2016 08:13:56 +0000https://111qqz.com/en/post/acm-icpc/2016/2016-09-15-cf220e/<p><a href="http://codeforces.com/problemset/problem/220/E" target="_blank" rel="noreferrer">题目链接</a></p> <p>题意：</p> <p>how many pairs of integers <em>l</em> and <em>r</em> are there, such that 1 ≤ <em>l</em> &lt; <em>r</em> ≤ <em>n</em> and sequence <em>b</em> = _a_1_a_2&hellip; <em>a__l__a__r__a__r</em> + 1&hellip; <em>a__n</em> has no more than <em>k</em> inversions.</p>codeforces 61 E. Enemy is weak (离散化+线段树求逆序三元组)https://111qqz.com/en/post/acm-icpc/2016/2016-09-05-cf61e/Mon, 05 Sep 2016 08:35:49 +0000https://111qqz.com/en/post/acm-icpc/2016/2016-09-05-cf61e/<p><a href="http://codeforces.com/problemset/problem/61/E" target="_blank" rel="noreferrer">题目链接</a> 题意：给出n个数，求满足 i&lt;j&lt;k且a[i]&gt;a[j]&gt;a[k]的三元组有多少个。</p>codeforces 459 D. Pashmak and Parmida's problem (离散化+线段树求逆序对数)https://111qqz.com/en/post/acm-icpc/2016/2016-09-05-cf459d/Mon, 05 Sep 2016 07:23:18 +0000https://111qqz.com/en/post/acm-icpc/2016/2016-09-05-cf459d/<p><a href="http://codeforces.com/problemset/problem/459/D" target="_blank" rel="noreferrer">题目链接</a> 题意：定义_f_(<em>l</em>, <em>r</em>, <em>x</em>)为区间[l,r]中x出现的次数。现在要求calculate the number of pairs of indicies <em>i</em>, <em>j</em> (1 ≤ <em>i</em> &lt; <em>j</em> ≤ <em>n</em>) such that_f_(1, <em>i</em>, <em>a__i</em>) &gt; <em>f</em>(<em>j</em>, <em>n</em>, <em>a__j</em>).</p>hdu 1394 Minimum Inversion Number (树状数组 逆序对)https://111qqz.com/en/post/acm-icpc/2015/2015-10-28-hdu1394/Wed, 28 Oct 2015 14:00:00 +0000https://111qqz.com/en/post/acm-icpc/2015/2015-10-28-hdu1394/<h1 class="relative group"> <div id="" class="anchor"></div> <span class="absolute top-0 w-6 transition-opacity opacity-0 -start-6 not-prose group-hover:opacity-100 select-none"> <a class="text-primary-300 dark:text-neutral-700 !no-underline" href="#" aria-label="Anchor">#</a> </span> </h1> <p><a href="http://acm.hdu.edu.cn/showproblem.php?pid=1394" target="_blank" rel="noreferrer">题目链接</a></p> <p>题意：</p> <p>这题是问一个长度为n的循环数组中，逆序对最少的个数。。。</p>