#include <queue>
void bfs(TreeNode* root) {
    if (root == NULL) return;

    queue<TreeNode*> q;
    q.push(root);
    while (!q.empty()) {
        ———————————————————————— // 在此处填入代码
        cout << node->val << " ";
        if (node->left) {
            q.push(node->left);
        }
        if (node->right) {
            q.push(node->right);
        }
    }
}