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Lowest Common Ancestor of a Binary Search Tree
思路：这题跟 Lowest Common Ancestor of Binary Tree 一模一样。思路：就是找p的节点在不在左支，或者右支，找到各自左右节点，然后进行比较，如果两者不一样，说明当前的root就是lowest 父节点，如果左边为空，那就都在右边，返回右边的即可，如果右边为空，那就都在左边，返回左边的即可。
/*** Definition for a binary tree node.* public class TreeNode {* int val;* TreeNode left;* TreeNode right;* TreeNode(int x) { val = x; }* }*/
class Solution {public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {if(root == null) {return null;}if(p == null || q == null) {return root;}TreeNode node = root;while(node != null) {if(node.val < p.val && node.val < q.val) {node = node.right;} else if(node.val > p.val && node.val > q.val) {node = node.left;} else {break;}}return node;}
}Lowest Common Ancestor of a Binary Tree
思路：lowestCommonAncestor 的定义就是找到的LCA；
如果两者都不为空，说明当前的root就是lowest 父节点，如果左边为空，那就都在右边，返回右边的即可，如果右边为空，那就都在左边，返回左边的即可。
/*** Definition for a binary tree node.* public class TreeNode {* int val;* TreeNode left;* TreeNode right;* TreeNode(int x) { val = x; }* }*/
class Solution {public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {if(root == null || root == p || root == q) {return root;}TreeNode leftnode = lowestCommonAncestor(root.left, p, q);TreeNode rightnode = lowestCommonAncestor(root.right, p, q);if(leftnode == null) {return rightnode;} else if(rightnode == null) {return leftnode;} else {return root;}}
}Lowest Common Ancestor of Deepest Leaves
- 题目要求求deepest leaf的LCA，我们首先需要tree depth的信息(注意不是node depth, 也可以理解为deepest leaf depth 也就是tree depth信息)，然后跟LCA一样，需要返回node信息，那么我们就需要resultType作为返回值；findLCA 表示当前枝，找到的LCA和它所能找到的deepest leaf 的depth；如果左右depth相等，证明当前node就是LCA；并返回leftnode的depth也就是deepest node的depth；
注意这里有两个表示：一个是method的depth代表node的depth，另外一个returnType里面的depth代表找到的node的 deepest depth；
/*** Definition for a binary tree node.* public class TreeNode {* int val;* TreeNode left;* TreeNode right;* TreeNode(int x) { val = x; }* }*/
class Solution {private class ReturnType {public TreeNode node;public int depth;public ReturnType(TreeNode node, int depth) {this.node = node;this.depth = depth;}}public TreeNode lcaDeepestLeaves(TreeNode root) {if(root == null) {return null;}ReturnType n = findLCA(root, 0);return n.node;}private ReturnType findLCA(TreeNode root, int depth) {if(root == null) {return new ReturnType(null, depth);}ReturnType leftnode = findLCA(root.left, depth + 1);ReturnType rightnode = findLCA(root.right, depth + 1);if(leftnode.depth == rightnode.depth) {return new ReturnType(root, leftnode.depth);}if(leftnode.depth > rightnode.depth) {return leftnode;} else {return rightnode;}}
}
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