[LeetCode] 98. Validate Binary Search Tree
2016-08-22 12:45
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思路:
in-order排序. 思路就是拿一个”全局”节点一直记录in-order顺序的上一个节点, 然后其他跟in-order遍历思路一模一样, 只不过把记录节点的步骤换为比较当前节点和上一个节点值而已.
in-order排序. 思路就是拿一个”全局”节点一直记录in-order顺序的上一个节点, 然后其他跟in-order遍历思路一模一样, 只不过把记录节点的步骤换为比较当前节点和上一个节点值而已.
bool helper(TreeNode* root, TreeNode*& prev) {
if (! root) return true;
if (! helper(root->left, prev))
return false;
if (prev && root->val <= prev->val)
return false;
prev = root;
return helper(root->right, prev);
}
bool isValidBST(TreeNode* root) {
TreeNode* prev = NULL;
return helper(root, prev);
}
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