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  • [leedcode 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.

    /**
     * Definition for a binary tree node.
     * public class TreeNode {
     *     int val;
     *     TreeNode left;
     *     TreeNode right;
     *     TreeNode(int x) { val = x; }
     * }
     */
    public class Solution {
        public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
            //借助二叉搜索树的性质,左子树小于根节点,右子树大于根节点的性质,对比p,q的值跟root值的关系,可得到下面的做法
            if(root==null||p==null||q==null) return null;
            if(p==root||q==root) return root;
            int temp=root.val;
            if(temp>p.val&&temp>q.val){
                return lowestCommonAncestor(root.left,p,q);
            }else if(temp<p.val&&temp<q.val)
                return lowestCommonAncestor(root.right,p,q);
            return root;
        }
    }
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  • 原文地址:https://www.cnblogs.com/qiaomu/p/4713661.html
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