题解 | #判断是不是二叉搜索树#中序遍历

/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 *	TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
#include <climits>
#include <iterator>
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @return bool布尔型
     */
    bool isValidBST(TreeNode* root) {
        // 因为不止需要判断是否比父母大 /小，还需要判断是否比祖先大/小，深度优先搜索
        deque<TreeNode*> workStack({root});
        TreeNode *cur,*previous=new TreeNode(-1),*lastVisited=new TreeNode(INT_MIN);
        previous->left=root;
        while(workStack.size()){
           cur=workStack.back();
           if(cur->left && (cur==previous->left||cur==previous->right)){
                workStack.push_back(cur->left);
           }else{
                workStack.pop_back();        
                if(cur->val<=lastVisited->val)return false;
                lastVisited=cur;
                if(cur->right)workStack.push_back(cur->right);
            }
        
            previous=cur;

        }
        return true;

    }
};