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  • [leetcode-235-Lowest Common Ancestor of a Binary Search Tree]

    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.

    思路:

    二叉查找树,左子树的值比根值小,右子树的值比根值大。如果p q都比root小,说明在左子树上,如果pq的值都比root大说明在右子树上,如果一左一右,则root即为所求。

    /**
     * Definition for a binary tree node.
     * struct TreeNode {
     *     int val;
     *     TreeNode *left;
     *     TreeNode *right;
     *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
     * };
     */
    class Solution {
    public:
        TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
            if (p -> val < root -> val && q -> val < root -> val)
                return lowestCommonAncestor(root -> left, p, q);
            if (p -> val > root -> val && q -> val > root -> val)
                return lowestCommonAncestor(root -> right, p, q);
            return root;
        }
    };

    参考:

    https://discuss.leetcode.com/topic/18614/easy-c-recursive-and-iterative-solutions

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  • 原文地址:https://www.cnblogs.com/hellowooorld/p/7678825.html
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