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2.16 Union Find docs 16

Union Find

  • 灵活使用并查集的思想,熟练掌握并查集的[模板]({{< relref "/ChapterThree/UnionFind.md" >}}),模板中有两种并查集的实现方式,一种是路径压缩 + 秩优化的版本,另外一种是计算每个集合中元素的个数 + 最大集合元素个数的版本,这两种版本都有各自使用的地方。能使用第一类并查集模板的题目有:第 128 题,第 130 题,第 547 题,第 684 题,第 721 题,第 765 题,第 778 题,第 839 题,第 924 题,第 928 题,第 947 题,第 952 题,第 959 题,第 990 题。能使用第二类并查集模板的题目有:第 803 题,第 952 题。第 803 题秩优化和统计集合个数这些地方会卡时间,如果不优化,会 TLE。
  • 并查集是一种思想,有些题需要灵活使用这种思想,而不是死套模板,如第 399 题,这一题是 stringUnionFind利用并查集思想实现的。这里每个节点是基于字符串和 map 的,而不是单纯的用 int 节点编号实现的。
  • 有些题死套模板反而做不出来,比如第 685 题,这一题不能路径压缩和秩优化,因为题目中涉及到有向图,需要知道节点的前驱节点,如果路径压缩了,这一题就没法做了。这一题不需要路径压缩和秩优化。
  • 灵活的抽象题目给的信息,将给定的信息合理的编号,使用并查集解题,并用 map 降低时间复杂度,如第 721 题,第 959 题。
  • 关于地图,砖块,网格的题目,可以新建一个特殊节点,将四周边缘的砖块或者网格都 union() 到这个特殊节点上。第 130 题,第 803 题。
  • 能用并查集的题目,一般也可以用 DFS 和 BFS 解答,只不过时间复杂度会高一点。
No. Title Solution Difficulty TimeComplexity SpaceComplexity Favorite Acceptance
0128 Longest Consecutive Sequence [Go]({{< relref "/ChapterFour/0100~0199/0128.Longest-Consecutive-Sequence.md" >}}) Medium O(n) O(n) ❤️ 48.0%
0130 Surrounded Regions [Go]({{< relref "/ChapterFour/0100~0199/0130.Surrounded-Regions.md" >}}) Medium O(m*n) O(m*n) 32.5%
0200 Number of Islands [Go]({{< relref "/ChapterFour/0200~0299/0200.Number-of-Islands.md" >}}) Medium O(m*n) O(m*n) 52.0%
0399 Evaluate Division [Go]({{< relref "/ChapterFour/0300~0399/0399.Evaluate-Division.md" >}}) Medium O(n) O(n) 55.9%
0547 Number of Provinces [Go]({{< relref "/ChapterFour/0500~0599/0547.Number-of-Provinces.md" >}}) Medium O(n^2) O(n) 62.2%
0684 Redundant Connection [Go]({{< relref "/ChapterFour/0600~0699/0684.Redundant-Connection.md" >}}) Medium O(n) O(n) 60.5%
0685 Redundant Connection II [Go]({{< relref "/ChapterFour/0600~0699/0685.Redundant-Connection-II.md" >}}) Hard O(n) O(n) 33.4%
0695 Max Area of Island [Go]({{< relref "/ChapterFour/0600~0699/0695.Max-Area-of-Island.md" >}}) Medium 68.1%
0721 Accounts Merge [Go]({{< relref "/ChapterFour/0700~0799/0721.Accounts-Merge.md" >}}) Medium O(n) O(n) ❤️ 54.2%
0765 Couples Holding Hands [Go]({{< relref "/ChapterFour/0700~0799/0765.Couples-Holding-Hands.md" >}}) Hard O(n) O(n) ❤️ 56.1%
0778 Swim in Rising Water [Go]({{< relref "/ChapterFour/0700~0799/0778.Swim-in-Rising-Water.md" >}}) Hard O(n^2) O(n) ❤️ 58.1%
0785 Is Graph Bipartite? [Go]({{< relref "/ChapterFour/0700~0799/0785.Is-Graph-Bipartite.md" >}}) Medium 49.6%
0803 Bricks Falling When Hit [Go]({{< relref "/ChapterFour/0800~0899/0803.Bricks-Falling-When-Hit.md" >}}) Hard O(n^2) O(n) ❤️ 33.1%
0839 Similar String Groups [Go]({{< relref "/ChapterFour/0800~0899/0839.Similar-String-Groups.md" >}}) Hard O(n^2) O(n) 44.1%
0924 Minimize Malware Spread [Go]({{< relref "/ChapterFour/0900~0999/0924.Minimize-Malware-Spread.md" >}}) Hard O(m*n) O(n) 41.8%
0928 Minimize Malware Spread II [Go]({{< relref "/ChapterFour/0900~0999/0928.Minimize-Malware-Spread-II.md" >}}) Hard O(m*n) O(n) ❤️ 41.8%
0947 Most Stones Removed with Same Row or Column [Go]({{< relref "/ChapterFour/0900~0999/0947.Most-Stones-Removed-with-Same-Row-or-Column.md" >}}) Medium O(n) O(n) 56.1%
0952 Largest Component Size by Common Factor [Go]({{< relref "/ChapterFour/0900~0999/0952.Largest-Component-Size-by-Common-Factor.md" >}}) Hard O(n) O(n) ❤️ 37.1%
0959 Regions Cut By Slashes [Go]({{< relref "/ChapterFour/0900~0999/0959.Regions-Cut-By-Slashes.md" >}}) Medium O(n^2) O(n^2) ❤️ 68.3%
0990 Satisfiability of Equality Equations [Go]({{< relref "/ChapterFour/0900~0999/0990.Satisfiability-of-Equality-Equations.md" >}}) Medium O(n) O(n) 48.9%
1020 Number of Enclaves [Go]({{< relref "/ChapterFour/1000~1099/1020.Number-of-Enclaves.md" >}}) Medium 60.8%
1202 Smallest String With Swaps [Go]({{< relref "/ChapterFour/1200~1299/1202.Smallest-String-With-Swaps.md" >}}) Medium 51.0%
1254 Number of Closed Islands [Go]({{< relref "/ChapterFour/1200~1299/1254.Number-of-Closed-Islands.md" >}}) Medium 62.7%
1319 Number of Operations to Make Network Connected [Go]({{< relref "/ChapterFour/1300~1399/1319.Number-of-Operations-to-Make-Network-Connected.md" >}}) Medium 56.3%
1579 Remove Max Number of Edges to Keep Graph Fully Traversable [Go]({{< relref "/ChapterFour/1500~1599/1579.Remove-Max-Number-of-Edges-to-Keep-Graph-Fully-Traversable.md" >}}) Hard 49.0%
1631 Path With Minimum Effort [Go]({{< relref "/ChapterFour/1600~1699/1631.Path-With-Minimum-Effort.md" >}}) Medium 51.0%
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