🌳 Binary Tree Patterns

// Inorder: Left → Root → Right
function inorder(root) {
    if (!root) return;
    inorder(root.left);
    visit(root);
    inorder(root.right);
}

// Preorder: Root → Left → Right
function preorder(root) {
    if (!root) return;
    visit(root);
    preorder(root.left);
    preorder(root.right);
}

// Postorder: Left → Right → Root
function postorder(root) {
    if (!root) return;
    postorder(root.left);
    postorder(root.right);
    visit(root);
}

function levelOrder(root) {
    if (!root) return [];
    
    const result = [];
    const queue = [root];
    
    while (queue.length > 0) {
        const levelSize = queue.length;
        const currentLevel = [];
        
        for (let i = 0; i < levelSize; i++) {
            const node = queue.shift();
            currentLevel.push(node.val);
            
            if (node.left) queue.push(node.left);
            if (node.right) queue.push(node.right);
        }
        
        result.push(currentLevel);
    }
    
    return result;
}

function hasPathSum(root, targetSum) {
    if (!root) return false;
    
    // Leaf node
    if (!root.left && !root.right) {
        return root.val === targetSum;
    }
    
    // Recurse with reduced sum
    const remaining = targetSum - root.val;
    return hasPathSum(root.left, remaining) || 
           hasPathSum(root.right, remaining);
}