验证二叉查找树

1
/ \
2   3
/
4
\
5

"{1,2,3,#,#,4,#,#,5}"

.

/**
* Definition of TreeNode:
* class TreeNode {
* public:
*     int val;
*     TreeNode *left, *right;
*     TreeNode(int val) {
*         this->val = val;
*         this->left = this->right = NULL;
*     }
* }
*/
class Solution {
public:
/**
* @param root: The root of binary tree.
* @return: True if the binary tree is BST, or false
*/
bool isValidBST(TreeNode *root) {
// write your code here
if (root == NULL)
{
return true;
}

if (root->left != NULL)
{
if (root->val <= root->left->val)
{
return false;
}

int leftMax = findMax(root->left);
if (root->val <= leftMax)
{
return false;
}
}

if (root->right != NULL)
{
if (root->val >= root->right->val)
{
return false;
}

int rightMin = findMin(root->right);
if (root->val >= rightMin)
{
return false;
}
}

return isValidBST(root->left) && isValidBST(root->right);
}
private:
int findMin(TreeNode *root)
{
TreeNode *p = root;
while (p->left != NULL)
{
p = p->left;
}

return p->val;
}

int findMax(TreeNode *root)
{
TreeNode *p = root;
while (p->right != NULL)
{
p = p->right;
}

return p->val;
}
};