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程式語言 - LeetCode - C++ - 107. Binary Tree Level Order Traversal II

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參考資訊：
https://www.cnblogs.com/grandyang/p/4051326.html

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:
    vector<vector<int>> levelOrderBottom(TreeNode* root) {
        queue<TreeNode*> q;
        vector<vector<int>> ans;

        if (!root) {
            return ans;
        }

        q.push(root);
        while (!q.empty()) {
            int size = q.size();
            vector<int> t;

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

                if (r->left) {
                    q.push(r->left);
                }
                if (r->right) {
                    q.push(r->right);
                }
                t.push_back(r->val);
            }

            ans.insert(ans.begin(), t);
        }

        return ans;
    }
};