Lowest Common Ancestor of a Binary Search Tree(树中两个结点的最低公共祖先)

题目描述：

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.

　　利用二叉排序树的性质，可以很好地解决这道题。

solution：

TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
    if (root == NULL || p == NULL || q == NULL)
        return NULL;

    if (root->val > p->val && root->val > q->val)
        return lowestCommonAncestor(root->left, p, q);
    else if (root->val < p->val && root->val < q->val)
        return lowestCommonAncestor(root->right, p, q);
    else 
        return root;
}

Lowest Common Ancestor of a Binary Search Tree(树中两个结点的最低公共祖先)

原文：http://www.cnblogs.com/gattaca/p/4674664.html