LeetCode: Validate Binary Search Tree

看了别人的代码

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool dfs(TreeNode *root, int MIN, int MAX) {
        if (!root) return true;
        if (root->val > MIN && root->val < MAX && dfs(root->left, MIN, root->val) && dfs(root->right, root->val, MAX))
            return true;
        else return false;
    }
    bool isValidBST(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        return dfs(root, INT_MIN, INT_MAX);
    }
};

 自己另外写了个，比较好懂

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    void dfs(TreeNode *root, TreeNode * &pre, bool &flag) {
        if (!root) return;
        dfs(root->left, pre, flag);
        if (pre && pre->val >= root->val) {
            flag = false;
            return;
        }
        pre = root;
        dfs(root->right, pre, flag);
    }
    bool isValidBST(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        TreeNode *pre = NULL;
        bool flag = true;
        dfs(root, pre, flag);
        return flag;
    }
};

 C#

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public bool IsValidBST(TreeNode root) {
        return dfs(root, Int64.MinValue, Int64.MaxValue);
    }
    public bool dfs(TreeNode root, Int64 Min, Int64 Max) {
        if (root == null) return true;
        return root.val > Min && root.val < Max && dfs(root.left, Min, root.val) && dfs(root.right, root.val, Max);
    }
}