DSA Sheet - Day 16 Binary Trees

🌳 DSA Sheet – Day 16: Binary Trees (Part 1)

This section introduces core binary tree concepts including DFS traversals, BFS level order traversal, and fundamental tree-based interview patterns.

📊 Progress Tracker

Progress: 0 / 6 Completed

Done	Problem	Practice	Level	Companies
	Preorder Traversal	Solve	Easy	Google, Microsoft
	Inorder Traversal	Solve	Easy	Amazon, Adobe
	Postorder Traversal	Solve	Easy	Google
	Level Order Traversal	Solve	Medium	Amazon, Uber
	Minimum Distance Between BST Nodes	Solve	Easy	Google
	Symmetric Tree	Solve	Easy	Microsoft, LinkedIn

🧠 Key Approaches

• Tree Traversals: DFS (Preorder, Inorder, Postorder)
• Level Order: BFS using queue
• Minimum Distance: Inorder traversal of BST (sorted)
• Symmetric Tree: Mirror comparison (left vs right)

⚡ Quick Cheatsheet

Inorder Traversal (DFS)

void inorder(TreeNode* root){
  if(!root) return;

  inorder(root->left);
  // visit node
  inorder(root->right);
}
    

Level Order Traversal (BFS)

queue q;
q.push(root);

while(!q.empty()){
  int size = q.size();

  while(size--){
    TreeNode* node = q.front(); 
    q.pop();

    if(node->left) q.push(node->left);
    if(node->right) q.push(node->right);
  }
}
    

Symmetric Tree

bool isMirror(TreeNode* a, TreeNode* b){
  if(!a && !b) return true;
  if(!a || !b) return false;

  return a->val == b->val &&
         isMirror(a->left, b->right) &&
         isMirror(a->right, b->left);
}
    

🔥 Pro Tip

Binary Trees revolve around two core patterns:

• DFS (recursive thinking)
• BFS (level-wise traversal)

If you master these two, most tree problems become pattern recognition.

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