LCA on 111qqz's bloghttps://111qqz.com/en/tags/lca/Recent content in LCA on 111qqz's blogHugo -- gohugo.ioen© 2015-2026 111qqzThu, 12 Oct 2017 13:44:29 +00002016-2017 ACM-ICPC, NEERC, Northern Subregional Contest G Gangsters in Central City (LCA)https://111qqz.com/en/post/acm-icpc/2017/2017-10-12-2016-neerc-subregional-g/Thu, 12 Oct 2017 13:44:29 +0000https://111qqz.com/en/post/acm-icpc/2017/2017-10-12-2016-neerc-subregional-g/<p>题意：</p> <p>有一棵树，水源在根节点1，房子在叶子节点。有若干操作，操作可能是歹徒占领或者离开一个房子。我们不想给歹徒供水，可以通过切断边实现（如果某个叶子节点到根节点的路径上有一条边被切掉，那么就不能供水了。）对于每次操作后，问不给所有歹徒供水最少要切多少条边，并且问在切满足前面最小的情况下，最少使得多少个良民受影响。初始没有歹徒。</p>hdu 3078 Network (LCA)https://111qqz.com/en/post/acm-icpc/2017/2017-07-30-hdu-3078/Sun, 30 Jul 2017 17:45:18 +0000https://111qqz.com/en/post/acm-icpc/2017/2017-07-30-hdu-3078/<p><a href="http://acm.hdu.edu.cn/showproblem.php?pid=3078" target="_blank" rel="noreferrer">题目链接</a></p> <h2 class="relative group">题意： <div id="题意" 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="#%e9%a2%98%e6%84%8f" aria-label="Anchor">#</a> </span> </h2> <p>一棵树，给出点权，问一条树链上第k大的点权，点权可以动态修改。</p>codeforces #425 D. Misha, Grisha and Underground (dfs+rmq在线求LCA,讨论了一年)https://111qqz.com/en/post/acm-icpc/2017/2017-07-30-codeforces-div2-425d/Sun, 30 Jul 2017 12:05:30 +0000https://111qqz.com/en/post/acm-icpc/2017/2017-07-30-codeforces-div2-425d/<p><a href="http://codeforces.com/contest/832/problem/D" target="_blank" rel="noreferrer">题目链接</a></p> <h2 class="relative group">题意： <div id="题意" 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="#%e9%a2%98%e6%84%8f" aria-label="Anchor">#</a> </span> </h2> <p>给出一棵树，以及三个点（可能重合），问两两组成的3条路径中，哪2条路径重合部分最长。</p>leetcode 235. Lowest Common Ancestor of a Binary Search Tree（求一个BST中某两个节点LCA）https://111qqz.com/en/post/acm-icpc/2017/2017-02-22-leetcode-235-lowest-common-ancestor-of-a-binary-search-tree/Wed, 22 Feb 2017 13:22:08 +0000https://111qqz.com/en/post/acm-icpc/2017/2017-02-22-leetcode-235-lowest-common-ancestor-of-a-binary-search-tree/<p><a href="https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/?tab=Description" target="_blank" rel="noreferrer">题目链接</a></p> <p>题意：求一个BST中某两个节点LCA&hellip;.</p> <p>思路：卧槽。。。竟然求LCA&hellip;直接想到的显然是Tarjan的方法或者。。。RMQ+DFS。。。但是感觉。。。leetcode怎么可能考算法。。。。于是想到。。。可以从BST下手。。。</p>zoj 3195 Design the city （lca,dfs+rmq）https://111qqz.com/en/post/acm-icpc/2016/2016-05-21-zoj-3195/Sat, 21 May 2016 08:31:20 +0000https://111qqz.com/en/post/acm-icpc/2016/2016-05-21-zoj-3195/<p><a href="http://www.icpc.moe/onlinejudge/showProblem.do?problemId=3320" target="_blank" rel="noreferrer">zoj 3195题目链接</a> 题意：求树上三点的最短距离。。。 思路：两两求，和除以2. 因为忘记初始化p=0..WA了将近两个小时。。。？ 妈的智障。</p>hdu 2874 Connections between cities (添加虚点，并查集+LCA(rmq+dfs))https://111qqz.com/en/post/acm-icpc/2016/2016-05-21-hdu-2874/Sat, 21 May 2016 04:58:22 +0000https://111qqz.com/en/post/acm-icpc/2016/2016-05-21-hdu-2874/<p><a href="http://acm.hdu.edu.cn/showproblem.php?pid=2874" target="_blank" rel="noreferrer">hdu2874题目链接</a></p> <p>题意：给一个森林，问两点的最短距离，或者输出两点不联通。</p> <p>思路：<strong>最最重要的一点是:添加虚点！</strong></p>poj 1986 Distance Queries (lca,在线做法dfs+rmq)https://111qqz.com/en/post/acm-icpc/2016/2016-05-20-poj-1986/Fri, 20 May 2016 11:25:49 +0000https://111qqz.com/en/post/acm-icpc/2016/2016-05-20-poj-1986/<p><a href="http://poj.org/problem?id=1986" target="_blank" rel="noreferrer">题目链接</a> 题意：求树上两点的最短距离？ 思路： dis[i]表示点i到根节点的距离，那么任意两点u,v的最短距离d = dis[u]+dis[v]-2*dis[LCA(u,v)]. 只需要求出rmq+dfs的在线方法求出lca(u,v)即可。</p>poj 1470 Closest Common Ancestors (lca,rmq+dfs,读入技巧)https://111qqz.com/en/post/acm-icpc/2016/2016-05-19-poj1470/Thu, 19 May 2016 08:42:05 +0000https://111qqz.com/en/post/acm-icpc/2016/2016-05-19-poj1470/<p><a href="http://poj.org/problem?id=1470" target="_blank" rel="noreferrer">poj1470题目链接</a></p> <p>题意：求两点的lca. 思路：dfs+rmq. 读入技巧。 读入比较坑爹。。。 学会了一种新的读入技巧。</p>poj 1330 Nearest Common Ancestors (lca,用dfs+rmq在线求解)https://111qqz.com/en/post/acm-icpc/2016/2016-05-19-poj1330/Thu, 19 May 2016 07:39:48 +0000https://111qqz.com/en/post/acm-icpc/2016/2016-05-19-poj1330/<p><a href="http://poj.org/problem?id=1330" target="_blank" rel="noreferrer">poj1330题目链接</a></p> <p>题意：给出一棵树，求两点的lca. 思路：将lca转化成rmq在线求解。</p>hdu 2586 How far away ？ (tarjan算法求LCA模板题)https://111qqz.com/en/post/acm-icpc/2016/2016-04-12-hdu2586/Tue, 12 Apr 2016 12:28:42 +0000https://111qqz.com/en/post/acm-icpc/2016/2016-04-12-hdu2586/<p><a href="http://acm.hdu.edu.cn/showproblem.php?pid=2586" target="_blank" rel="noreferrer">题目链接</a> 题意：一棵树，给出n-1个边权，然后q组查询，每组查询询问两个点之间的距离。 思路：</p>