并查集

我们可以在一开始把每个元素都看成一棵树，并且根结点的父结点指向自己，在此基础上完成查找、合并操作。

两种优化方法：第一种按秩合并，即每次都把较矮的树并到较高的树中。第二种路径压缩，即让所有的并入的结点都指向整棵树的根结点。

具体代码如下：

 1 //并查集
 2 class DisjointSet {
 3 private:
 4     //rank is the height of tree
 5     int *father, *rank;
 6 public:
 7     DisjointSet(int size) {
 8         father = new int[size];
 9         rank = new int[size];
10         for (int i = 0; i < size; ++i) {
11             //initially every node is a tree so father points to itself
12             father[i] = i;
13             rank[i] = 0;
14         }
15     }
16     ~DisjointSet() {
17         delete[] father;
18         delete[] rank;
19     }
20     int find_set(int node) {
21         if (father[node] != node) {
22             //path compression
23             father[node]=find_set(father[node]);
24         }
25         return father[node];
26     }
27     bool merge(int node1, int node2) {
28         int ancestor1 = find_set(node1);
29         int ancestor2 = find_set(node2);
30         if (ancestor1 != ancestor2) {
31             //rank merge
32             if (rank[ancestor1] > rank[ancestor2]) {
33                 swap(ancestor1, ancestor2);
34             }
35             //shorter tree points to higher tree
36             father[ancestor1] = ancestor2;
37             rank[ancestor2] = max(rank[ancestor2], rank[ancestor1] + 1);
38             return true;
39         }
40         return false;
41     }
42 };

 

转载于:https://www.cnblogs.com/NoviScl/p/7112627.html