Validate Binary Search Tree

Given a binary tree, determine if it is a valid binary search tree (BST).

Assume a BST is defined as follows:

• The left subtree of a node contains only nodes with keys less than the node's key.
• The right subtree of a node contains only nodes with keys greater than the node's key.
• Both the left and right subtrees must also be binary search trees.

Example 1:

    2   / \  1   3

Binary tree [2,1,3], return true.

Example 2:

    1   / \  2   3

Binary tree [1,2,3], return false.

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     struct TreeNode *left; *     struct TreeNode *right; * }; */int nums[100000];int count = 0;// 中序遍历void middle_traverse(struct TreeNode* root) {    if (root != NULL) {        middle_traverse(root->left);        nums[count++] = root->val;        middle_traverse(root->right);    }}bool isValidBST(struct TreeNode* root) {    middle_traverse(root);    int i;    for (i = 0; i < count - 1; ++i) {        if (nums[i] >= nums[i + 1]) {            count = 0;            return false;        }    }    count = 0;    return true;}

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