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235. Lowest Common Ancestor of a Binary Search Tree

时间:2015-07-31 06:35:43      阅读:152      评论:0      收藏:0      [点我收藏+]

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) {

    //make sure p.val < q.val
    if (p.val > q.val) {
      TreeNode tmp = p;
      p = q;
      q = tmp;
    }
    if (root.val == p.val || root.val == q.val) {
      return root;
    }
    if (root.val > p.val && root.val < q.val) {
      return root;
    }
    if (root.val < p.val) {
      return lowestCommonAncestor(root.right, p, q);
    }
    return lowestCommonAncestor(root.left, p, q);
  }
}

235. Lowest Common Ancestor of a Binary Search Tree

原文:http://www.cnblogs.com/shini/p/4691090.html

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