validate-binary-search-tree

最新推荐文章于 2019-06-19 22:40:03 发布

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最新推荐文章于 2019-06-19 22:40:03 发布

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分类专栏：数据结构二叉树

本文链接：https://blog.youkuaiyun.com/linking_lin/article/details/86482843

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本文探讨了如何判断一个二叉树是否为有效的二叉搜索树（BST）。通过中序遍历的方法，确保节点值在遍历过程中递增，以此来验证二叉树是否符合BST的定义。

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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.

OJ's Binary Tree Serialization:

The serialization of a binary tree follows a level order traversal, where '#' signifies a path terminator where no node exists below.

Here's an example:

The above binary tree is serialized as"{1,2,3,#,#,4,#,#,5}".

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
/*wrong:
        if(NULL == root){
            return true;
        }else if(root->left && root->right){
            if(!(root->left->val < root->val && root->val < root->right->val)){
                return false;
            }else{
                return isValidBST(root->left)&&isValidBST(root->right);
            }
        }else if(!root->left && !root->right){
            return true;
        }else if(root->left){
            if(root->left->val < root->val){
                return isValidBST(root->left);
            }else{
                return false;
            }            
        }else{
            if(root->right->val > root->val){
                return isValidBST(root->right);
            }else{
                return false;
            } 
        }
*/
    int val_arr[1000];
    int index = 0;
    void inorder_tra(TreeNode *root){
        if(root==NULL){
            return;
        }
        inorder_tra(root->left);
        val_arr[index++] = root->val;
        inorder_tra(root->right);
    }
    
    bool isValidBST(TreeNode *root) {
        inorder_tra(root);
//        printf("%d\n",index);
        if(index == 1){
            return true;
        }else{
            for(int i=1;i<index;++i){
                if(val_arr[i-1]>=val_arr[i]){
                    return false;
                }
            }
            return true;
        }
    }
};