bfs.cpp

#include <iostream>
#include <queue>

using namespace std;

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) {}
};

void BFS(TreeNode* root) {
    if (root == nullptr) return;

    queue<TreeNode*> q;
    q.push(root);

    while (!q.empty()) {
        TreeNode* node = q.front();
        q.pop();

        cout << node->val << " ";
        cout << q.size() << '\n'; 
        if (node->left != nullptr) q.push(node->left);
        if (node->right != nullptr) q.push(node->right);
    }
}

int main() {
    TreeNode* root = new TreeNode(1);
    root->left = new TreeNode(2);
    root->right = new TreeNode(3);
    root->left->left = new TreeNode(4);
    root->left->right = new TreeNode(5);
    root->right->left = new TreeNode(6);
    root->right->right = new TreeNode(7); 
    root->left->left->right = new TreeNode(8);
    root->right->right->right = new TreeNode(9); 
    cout << "BFS traversal: ";
    BFS(root);

    return 0;
}