Leetcode 235. Lowest Common Ancestor of a Binary Search Tree

最新推荐文章于 2022-10-04 11:47:29 发布

原创最新推荐文章于 2022-10-04 11:47:29 发布 · 194 阅读

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本文介绍了一种寻找二叉搜索树中两个节点的最低公共祖先的有效算法，并提供了简洁的实现代码。

Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.

According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes v and w as the lowest node in T that has both v and w as descendants (where we allow a node to be a descendant of itself).”

        _______6______
       /              \
    ___2__          ___8__
   /      \        /      \
   0      _4       7       9
         /  \
         3   5

For example, the lowest common ancestor (LCA) of nodes 2 and 8 is 6. Another example is LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition.

我的解法

几乎一次通过，都没想到自己能这么快做出来，有点快质的飞跃了呢

public class Solution {
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
        int max = Math.max(p.val, q.val);
        int min = Math.min(p.val, q.val);
        
        if(root.val == p.val || root.val == q.val || (root.val < max && root.val > min)){
            return root;
        }
        else if(root.val > max && root.left != null){
            root = lowestCommonAncestor(root.left, p, q);
        }
        else{
            root = lowestCommonAncestor(root.right, p, q);
        }
        return root;
    }
}

discuss精炼解法

public class Solution {
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
        if(root.val > p.val && root.val > q.val){
            return lowestCommonAncestor(root.left, p, q);
        }else if(root.val < p.val && root.val < q.val){
            return lowestCommonAncestor(root.right, p, q);
        }else{
            return root;
        }
    }
}