missjing/leetcode

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 problem： 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. confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ. ---------------------------------------------------------------------------------------- solution： //对每个结点，判断其值是否在左右界中，并实时更新界， //比如遍历到根节点的左孩子结点，它的上界是根节点的值；遍历到根节点的右孩子结点，它的下界是根节点的值 ///////////////////////////////////// struct TreeNode { int val; TreeNode *left; TreeNode *right; TreeNode(int x) : val(x), left(NULL), right(NULL) {} }; bool isValidBST_aux(TreeNode *node, int leftVal, int rightVal) { if(node == NULL) return true; return leftVal < node->val && rightVal > node->val && isValidBST_aux(node->left, leftVal, node->val) && isValidBST_aux(node->right, node->val, rightVal); } bool isValidBST(TreeNode *root) { return isValidBST_aux(root, INT_MIN, INT_MAX); }