235. Lowest Common Ancestor of a Binary Search Tree

最新推荐文章于 2022-02-12 22:47:33 发布

无名_1989

最新推荐文章于 2022-02-12 22:47:33 发布

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文章标签： Tree

本文链接：https://blog.youkuaiyun.com/dongyu_1989/article/details/79249905

本文介绍了一种在二叉搜索树中寻找两个指定节点的最低公共祖先的方法。通过递归遍历树结构，当根节点为其中一个目标节点或为空时直接返回该节点；若目标节点分别位于根节点两侧，则当前根节点即为所求。

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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.

class Solution {
public:
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
        if(root==NULL || root==p || root==q)
            return root;
        TreeNode *left = lowestCommonAncestor(root->left, p, q);
        TreeNode *right = lowestCommonAncestor(root->right, p, q);
        if(left&&right)
            return root;
        else 
            return left ? left : right;
    }
};