算法树中两个结点的最低公共祖结点
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1. 概述
树的最低公共祖结点,即从根结点开始到两个给定的结点,会形成两条对应的路径,即这两条路径最低的交汇点。
如下图所示的树,8结点和11结点的最低公共祖结点是5结点。
2. 思路
思路:
1)提供一个方法,分别从根结点开始向下查找到对应的给定结点,得到对应的路径;
2)从上面得到的两条路径中,查找到最近的交汇点。
从上图可以得到两条路径的第一个交汇点为结点5,即为最低公共祖结点
3. 代码及测试
Java
package cn.pku.edu.algorithm.leetcode.plus;
import cn.pku.edu.algorithm.leetcode.common.TreeNode;
import java.util.ArrayList;
import java.util.List;
/**
* @author allen
* @date 2022/9/19
*/
public class LastCommonParent
public static void main(String[] args)
LastCommonParent lastCommonParent = new LastCommonParent();
TreeNode root = new TreeNode(1);
TreeNode treeNode2 = new TreeNode(2);
TreeNode treeNode3 = new TreeNode(3);
TreeNode treeNode4 = new TreeNode(4);
TreeNode treeNode5 = new TreeNode(5);
TreeNode treeNode6 = new TreeNode(6);
TreeNode treeNode7 = new TreeNode(7);
TreeNode treeNode8 = new TreeNode(8);
TreeNode treeNode9 = new TreeNode(9);
TreeNode treeNode10 = new TreeNode(10);
TreeNode treeNode11 = new TreeNode(11);
root.left = treeNode2;
root.right = treeNode3;
treeNode2.left = treeNode4;
treeNode2.right = treeNode5;
treeNode3.right = treeNode6;
treeNode4.left = treeNode7;
treeNode5.left = treeNode8;
treeNode5.right = treeNode9;
treeNode8.left = treeNode10;
treeNode9.right = treeNode11;
TreeNode last = lastCommonParent.getLastCommonParent(root, treeNode8, treeNode11);
if (last != null)
System.out.println(last.val);
else
System.out.println("last common parent is null");
public TreeNode getLastCommonParent(TreeNode root, TreeNode node1, TreeNode node2)
if (root == null || node1 == null || node2 == null)
return null;
List<TreeNode> path1 = new ArrayList<>();
getNodePath(root, node1, path1);
List<TreeNode> path2 = new ArrayList<>();
getNodePath(root, node2, path2);
return getLastCommonNode(path1, path2);
private boolean getNodePath(TreeNode root, TreeNode node, List<TreeNode> path)
// 到达了指定结点
if (root == node)
path.add(root);
return true;
path.add(root);
boolean found = false;
if (root.left != null)
found = getNodePath(root.left, node, path);
if (!found && root.right != null)
found = getNodePath(root.right, node, path);
// 以本结点为根节点的子树中未找到指定结点,则将本结点从路径中去掉
if (!found)
path.remove(path.size() - 1);
return found;
private TreeNode getLastCommonNode(List<TreeNode> path1, List<TreeNode> path2)
int n = path1.size();
TreeNode last = null;
for (int i = 0; i < n; i++)
TreeNode node1 = path1.get(i);
TreeNode node2 = path2.get(i);
if (node1 != node2)
break;
last = node1;
return last;
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