dsa3 min read
Delete Node in a BST
Find and delete a node from a BST while maintaining BST properties using in-order successor.
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Trees
54 articles
dsa2 min read
Flatten Binary Tree to Linked List
Flatten a binary tree to a linked list in-place using pre-order traversal order.
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dsa2 min read
Populating Next Right Pointers in Each Node
Connect each node to its next right node using BFS level order or O(1) space pointer manipulation.
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dsa3 min read
All Nodes Distance K in Binary Tree
Find all nodes at distance K from a target node by building parent pointers then doing BFS.
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dsa2 min read
Sum Root to Leaf Numbers
Compute the total sum of all root-to-leaf numbers formed by concatenating digits along each path.
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dsa3 min read
Maximum Width of Binary Tree
Find the maximum width of a binary tree where width is measured from leftmost to rightmost non-null node per level.
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dsa2 min read
Count Good Nodes in Binary Tree
Count nodes where no node on the root-to-node path has a value greater than the node itself.
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Convert BST to Greater Tree
Replace each node value with the sum of all values greater than or equal to it using reverse in-order traversal.
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Find Duplicate Subtrees
Find all duplicate subtrees by serializing each subtree and using a hash map to detect duplicates.
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Unique Binary Search Trees II
Generate all structurally unique BSTs with values 1 to n using divide and conquer with memoization.
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Trim a Binary Search Tree
Trim a BST so all values lie within [low, high] by recursively pruning out-of-range subtrees.
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dsa3 min read
Serialize and Deserialize BST
Serialize a BST to a compact preorder string and reconstruct it using the min-max BST property.
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Vertical Order Traversal of a Binary Tree
Group tree nodes by vertical column then row, sorting by value within same position using BFS with coordinates.
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dsa3 min read
Step-By-Step Directions From a Binary Tree Node to Another
Find path directions between two tree nodes by finding LCA then building paths from LCA to each target.
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Check Completeness of a Binary Tree
Verify a binary tree is complete using BFS: once a null child is seen, no more non-null nodes should follow.
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Recover Binary Search Tree
Find and swap the two misplaced nodes in a BST using in-order traversal to detect the violations.
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House Robber III
Maximize robbery from a tree-structured neighborhood where adjacent (parent-child) nodes cannot both be robbed.
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Binary Tree Cameras
Find minimum cameras to monitor all nodes using greedy bottom-up: prefer placing cameras at parents of uncovered leaves.
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Distribute Coins in Binary Tree
Count minimum moves to distribute coins evenly by tracking excess/deficit coins flowing through each edge.
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dsa3 min read
Kth Ancestor of a Tree Node
Find the Kth ancestor of any tree node in O(log k) per query using binary lifting (sparse table DP).
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Binary Tree Maximum Path Sum
Find the maximum path sum in a binary tree where the path can start and end at any node.
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Serialize and Deserialize Binary Tree
Serialize a binary tree to string and back using BFS level-order or DFS preorder with null markers.
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Maximum Sum BST in Binary Tree
Find the maximum sum of any BST subtree within a binary tree using post-order DFS returning subtree metadata.
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Construct Binary Search Tree from Preorder Traversal
Reconstruct a BST from its preorder traversal in O(n) using min-max bounds to place each node.
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Find Leaves of Binary Tree
Collect leaves by height (distance from leaf) repeatedly, returning all leaves at each height level.
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Count Complete Tree Nodes
Count nodes in a complete binary tree in O(log^2 n) by comparing left and right heights to identify full subtrees.
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Minimum Time to Collect All Apples in a Tree
Find minimum seconds to collect all apples in a tree by DFS: include a subtree path only if it contains apples.
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Maximum Difference Between Node and Ancestor
Find the maximum |a - b| for any ancestor-descendant pair by tracking min and max values along each root-to-leaf path.
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Longest ZigZag Path in Binary Tree
Find the longest zigzag path in a binary tree where you alternate left-right directions at each step.
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dsa3 min read
Sum of Distances in Tree
Compute sum of distances from every node to all others in O(n) using two DFS passes with rerooting technique.
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Unique Binary Search Trees
Count the number of structurally unique BSTs with n nodes using Catalan numbers and DP.
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N-ary Tree Level Order Traversal
Perform level-order traversal of an N-ary tree using BFS, collecting all children at each level.
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dsa1 min read
Binary Tree Pruning
Remove all subtrees that do not contain a 1 by recursively returning null for subtrees with only zeros.
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Maximum Level Sum of a Binary Tree
Find the level with the maximum sum using BFS level-order traversal to compute each level's total.
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Smallest String Starting From Leaf
Find lexicographically smallest string from any leaf to root by collecting and comparing reversed paths.
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Amount of Time for Binary Tree to Be Infected
Find time for infection to spread through entire tree from a start node by converting to graph then doing BFS.
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dsa3 min read
Minimum Number of Operations to Sort Binary Tree by Level
Find minimum swaps to sort each level of a binary tree using BFS and cycle-detection in permutation sorting.
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Binary Search Tree Iterator
Implement an in-order BST iterator with O(h) space using a stack to simulate recursive in-order traversal.
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Path Sum IV
Sum all root-to-leaf path sums in a tree encoded as 3-digit integers using a hashmap to decode tree structure.
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Closest Binary Search Tree Value II
Find k values closest to target in a BST using two in-order iterators (forward and reverse) with a two-pointer merge.
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Binary Tree Upside Down
Transform a binary tree so every right child becomes a sibling and left child becomes parent using iterative rotation.
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dsa1 min read
Inorder Successor in BST II
Find the inorder successor of a node in a BST when you have access to parent pointers.
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Second Minimum Node In a Binary Tree
Find second minimum value in a special binary tree where root is min and each node equals min of its children.
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Construct String from Binary Tree
Build a preorder string representation of a binary tree using parentheses to show tree structure.
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Add One Row to Tree
Insert a new row of nodes at a given depth in a binary tree using BFS to reach the target depth level.
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Deepest Leaves Sum
Sum all nodes at the deepest level of a binary tree using BFS to process level by level.
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Cousins in Binary Tree
Determine if two nodes are cousins (same depth, different parents) using BFS to track depth and parent.
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Number of Nodes in a Complete Binary Tree (Optimized)
Count nodes in complete binary tree in O(log^2 n) by comparing left vs right subtree heights recursively.
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dsa1 min read
Insert into a Binary Search Tree
Insert a value into a BST by traversing left/right based on comparisons until reaching a null position.
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dsa2 min read
N-ary Tree Preorder and Postorder Traversal
Traverse an N-ary tree in preorder and postorder using DFS with a stack or recursion.
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Construct Quad Tree
Build a quad tree from a 2D grid by recursively checking if a region is uniform and splitting into four quadrants.
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dsa1 min read
Increasing Order Search Tree
Rearrange a BST into a right-skewed tree with no left children using in-order traversal.
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dsa1 min read
Count Nodes Equal to Average of Subtree
Count nodes where node value equals the average of all values in its subtree using post-order DFS returning sum and count.
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dsa4 min read
Trees — Master Recap & Pattern Cheatsheet
Complete Trees section recap covering 9 core patterns, complexity guide, and interview problem index.
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