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.
做这道题，首先得了解二叉排序树的性质，然后就是利用队列去记录寻找到q或者p的路径，然后对路径进行遍历，找到分叉点，这个分叉点就是要找的点。
public void findPath(TreeNode root, TreeNode p,Queue<TreeNode> queue)
{
TreeNode temp=root;
while(temp!=null && temp.val!=p.val)
{
queue.offer(temp);
if(temp.val>p.val) temp=temp.left;
else temp=temp.right;
}
queue.add(p);
}
public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
Queue<TreeNode> pQ=new LinkedList<TreeNode>();
Queue<TreeNode> qQ=new LinkedList<TreeNode>();
findPath(root, p, pQ);
findPath(root, q, qQ);
TreeNode x1=null;
TreeNode x2=null;
TreeNode anc=null;
while(!pQ.isEmpty() && !qQ.isEmpty())
{
x1=pQ.poll();
x2=qQ.poll();
if(x1.val==x2.val)
{
anc=x1;
}
else
{
break;
}
}
return anc;
}
[LeetCode] Lowest Common Ancestor of a Binary Search Tree
原文：http://www.cnblogs.com/maydow/p/4640941.html