BFS (Level Order Traversal)

Key Signals & Indicators

• Need to traverse a tree layer-by-layer (level order)
• Finding short paths, boundary structures, level stats
• Requires tracking values grouped by height level

// C++ Tree Level Order BFS Template
#include <vector>
#include <queue>

struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
};

std::vector<std::vector<int>> levelOrderBFS(TreeNode* root) {
    if (!root) return {};
    
    std::vector<std::vector<int>> result;
    std::queue<TreeNode*> q;
    q.push(root);
    
    while (!q.empty()) {
        int levelSize = q.size();
        std::vector<int> currentLevel;
        
        for (int i = 0; i < levelSize; ++i) {
            TreeNode* node = q.front();
            q.pop();
            currentLevel.push_back(node->val);
            
            if (node->left) q.push(node->left);
            if (node->right) q.push(node->right);
        }
        result.push_back(currentLevel);
    }
    return result;
}