最大独立集问题


当树中任何两个节点间没有边时,独立集就是所有二叉树节点的子集。 

现在将从一组元素中找到最长的独立集。例如,如果元素用于形成二叉树,那么所有最大的子集,其中该子集中的元素彼此不连接。

输入和输出

Input:
A binary tree.

Output:
Size of the Largest Independent Set is: 5

算法

longSetSize(root)

在此算法中,将形成二叉树,该树的每个节点都将保存数据和 setSize。

输入 − 二叉树的根节点。

输出 −最长集合的大小。

Begin
   if root = φ, then
      return 0
   if setSize(root) ≠ 0, then
      setSize(root)
   if root has no child, then
      setSize(root) := 1
      return setSize(root)
   setSizeEx := longSetSize(left(root)) + longSetSize(right(root)) //excluding root
   setSizeIn := 1

   if left child exists, then
      setSizeIn := setSizeIn + longSetSize(left(left(root))) + longSetSize(left(right(root)))

   if right child exists, then
      setSizeIn := setSizeIn + longSetSize(right(left(root))) + longSetSize(right(right(root)))

   if setSizeIn > setSizeEx, then
      setSize(root) := setSizeIn
   else
      setSize(root) := setSizeEx

   return setSize(root)
End

示例

#include <iostream>
using namespace std;

struct node {
   int data;
   int setSize;
   node *left, *right;
};

int longSetSize(node *root) {
   if (root == NULL)
      return 0;

   if (root->setSize != 0)
      return root->setSize;

   if (root->left == NULL && root->right == NULL)    //when there is no child
      return (root->setSize = 1);

   // set size exclusive root is set size of left and set size of right

   int setSizeEx = longSetSize(root->left) + longSetSize(root->right);
   int setSizeIn = 1;             //inclusive root node

   if (root->left)               //if left sub tree is present
      setSizeIn += longSetSize(root->left->left) + longSetSize(root->left->right);

   if (root->right)                //if right sub tree is present
      setSizeIn += longSetSize(root->right->left) +longSetSize(root->right->right);
   root->setSize = (setSizeIn>setSizeEx)?setSizeIn:setSizeEx;

   return root->setSize;
}

struct node* getNode(int data) {          //create a new node with given data
   node* newNode = new node;
   newNode->data = data;
   newNode->left = newNode->right = NULL;
   newNode->setSize = 0;

   return newNode;
}

int main() {
   node *root = getNode(20);
   root->left = getNode(8);
   root->left->left = getNode(4);
   root->left->right = getNode(12);
   root->left->right->left = getNode(10);
   root->left->right->right = getNode(14);
   root->right = getNode(22);

   root->right->right = getNode(25);
   cout << "Size of the Largest Independent Set is: " << longSetSize(root);
}

输出

Size of the Largest Independent Set is − 5

更新日期: 2020 年 6 月 16 日

334 次浏览

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