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1305. All Elements in Two Binary Search Trees

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Symbols count in article: 2.3k Reading time ≈ 2 mins.

173. Binary Search Tree Iterator O(n) time O(h) space

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<int> getAllElements(TreeNode* root1, TreeNode* root2) {
        pushAllLeft(root1, s1);
        pushAllLeft(root2, s2);
        vector<int> res;
        while (!s1.empty() || !s2.empty()) {
            auto p = s1.empty() ? INT_MAX : s1.top()->val;
            auto q = s2.empty() ? INT_MAX : s2.top()->val;
            int mn = min(p, q);
            if (p == mn) {
                res.push_back(p);
                pushAllLeft(s1.top()->right, s1);
            }
            if (q == mn) {
                res.push_back(q);
                pushAllLeft(s2.top()->right, s2);
            }
        }
        return res;
    }

    void pushAllLeft(TreeNode *p, stack<TreeNode *> &s) {
        if (!s.empty()) { // 注意判空，因为一开始push的时候是空的
            s.pop();
        }
        while (p) {
            s.push(p);
            p = p->left;
        }
    }

    stack<TreeNode *> s1, s2;
};
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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<int> getAllElements(TreeNode* root1, TreeNode* root2) {
        pushAllLeft(root1, s1);
        pushAllLeft(root2, s2);
        vector<int> res;
        while (!s1.empty() || !s2.empty()) {
            auto p = s1.empty() ? nullptr : s1.top();
            auto q = s2.empty() ? nullptr : s2.top();
            if (p && q) {
                if (p->val <= q->val) {
                    res.push_back(p->val);
                    pushAllLeft(p->right, s1);
                } else {
                    res.push_back(q->val);
                    pushAllLeft(q->right, s2);
                }
            } else if (p) {
                res.push_back(p->val);
                pushAllLeft(p->right, s1);
            } else {
                res.push_back(q->val);
                pushAllLeft(q->right, s2);
            }
        }
        return res;
    }

    void pushAllLeft(TreeNode *p, stack<TreeNode *> &s) {
        if (!s.empty()) { // 注意判空，因为一开始push的时候是空的
            s.pop();
        }
        while (p) {
            s.push(p);
            p = p->left;
        }
    }

    stack<TreeNode *> s1, s2;
};