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Copy path二叉树的最近公共祖先.java
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82 lines (62 loc) · 2.94 KB
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package io.github.dunwu.algorithm.tree.btree;
import io.github.dunwu.algorithm.tree.TreeNode;
import org.junit.jupiter.api.Assertions;
/**
* <a href="https://leetcode-cn.com/problems/lowest-common-ancestor-of-a-binary-tree/">236. 二叉树的最近公共祖先</a>
* <a
* href="https://leetcode-cn.com/problems/lowest-common-ancestor-of-a-binary-tree/solution/er-cha-shu-de-zui-jin-gong-gong-zu-xian-by-leetc-2/">解题思路</a>
*
* @author <a href="mailto:forbreak@163.com">Zhang Peng</a>
* @date 2020-01-28
*/
public class 二叉树的最近公共祖先 {
public static void main(String[] args) {
Solution s = new Solution();
TreeNode input = TreeNode.buildTree(6, 2, 8, 0, 4, 7, 9, null, null, 3, 5);
TreeNode output1 = s.lowestCommonAncestor(input, TreeNode.find(input, 2), TreeNode.find(input, 8));
Assertions.assertNotNull(output1);
Assertions.assertEquals(6, output1.val);
TreeNode output2 = s.lowestCommonAncestor(input, TreeNode.find(input, 2), TreeNode.find(input, 4));
Assertions.assertNotNull(output2);
Assertions.assertEquals(2, output2.val);
Solution2 s2 = new Solution2();
TreeNode input2 = TreeNode.buildTree(6, 2, 8, 0, 4, 7, 9, null, null, 3, 5);
TreeNode output3 = s2.lowestCommonAncestor(input2, TreeNode.find(input2, 2), TreeNode.find(input2, 8));
Assertions.assertNotNull(output3);
Assertions.assertEquals(6, output3.val);
TreeNode output4 = s2.lowestCommonAncestor(input2, TreeNode.find(input2, 2), TreeNode.find(input2, 4));
Assertions.assertNotNull(output4);
Assertions.assertEquals(2, output4.val);
}
static class Solution {
public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
if (root == null) return null;
if (root == p || root == q) return root;
TreeNode left = lowestCommonAncestor(root.left, p, q);
TreeNode right = lowestCommonAncestor(root.right, p, q);
if (left != null && right != null) { return root; }
return left != null ? left : right;
}
}
static class Solution2 {
private TreeNode res = null;
public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
res = null;
return find(root, p.val, q.val);
}
TreeNode find(TreeNode root, int p, int q) {
if (root == null) { return null; }
// 如果已经找到 LCA 节点，直接返回
if (res != null) { return res; }
if (root.val == p || root.val == q) return root;
TreeNode left = find(root.left, p, q);
TreeNode right = find(root.right, p, q);
if (left != null && right != null) {
// 当前节点是 LCA 节点，记录下来
res = root;
return res;
}
return left != null ? left : right;
}
}
}