二叉树专题

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struct TreeNode {
    int val;
    TreeNode *left, *right;
    TreeNode(int x): val(x), left(nullptr), right(nullptr) {}
    TreeNode(int x, TreeNode *left, TreeNode *right): val(x), left(left), right(right) {}
};

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// 先序建立二叉树，返回根节点，空节点用 0 表示
TreeNode* createBiTree(TreeNode *root) {
    int val;
    cin >> val;
    if (val) {
        root = new TreeNode(val);
        root->left = createBiTree(root->left);
        root->right = createBiTree(root->right);
    }
    return root;
}

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