Steward

分享是一種喜悅、更是一種幸福

程式語言 - LeetCode - C++ - 2196. Create Binary Tree From Descriptions

---

題目：


解答：

/**
 * 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:
    TreeNode* createBinaryTree(vector<vector<int>>& descriptions) {
        int n = descriptions.size();
        unordered_map<int, vector<pair<int, int>>> mp;

        for (auto& p : descriptions) {
            mp[p[0]].push_back({ p[1], p[2]});
        }

        int root = -1;

        for (auto& p : descriptions) {
            bool found = true;

            for (auto& c : descriptions) {
                if (p[0] == c[1]) {
                    found = false;
                    break;
                }
            }

            if (found) {
                root = p[0];
                break;
            }
        }

        TreeNode* r = new TreeNode(root);
        queue<TreeNode*> q;

        q.push(r);

        while (!q.empty()) {
            int size = q.size();

            for (int i = 0; i < size; ++i) {
                TreeNode* n = q.front();

                q.pop();

                for (auto& it : mp[n->val]) {
                    if (it.second) {
                        n->left = new TreeNode(it.first);
                        q.push(n->left);
                    }
                    else {
                        n->right = new TreeNode(it.first);
                        q.push(n->right);
                    }
                }
            }
        }

        return r;
    }
};