Tree pattern

Union-Find array/structure Array for Union-Find structure Sorting edges by weight Leveraging MST properties for edge criticality Graph theory (MST) Algorithm design

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05.08.2023

medium

95. Unique Binary Search Trees II

Kotlin

All possible Binary Search Trees for 1..n numbers

Tree Backtracking Binary Search

stack tree backtracking dfs bitmask hash_set

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23.07.2023

medium

894. All Possible Full Binary Trees

Kotlin

All possible Full Binary Trees with n nodes, each have both children

Tree

binary_tree hash_set breadth_first_search recursion string_hashing bfs

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12.07.2023

medium

863. All Nodes Distance K in Binary Tree

Kotlin

List of k distanced from target nodes in a Binary Tree

Graph Tree

fromTo visited dfs bfs undirected graph construction and BFS binary tree

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11.07.2023

easy

111. Minimum Depth of Binary Tree

Kotlin

Count nodes in the shortest path from root to leaf

Graph Tree

ArrayDeque Binary Tree Breadth-First Search BFS for level counting Tree Traversal

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16.06.2023

hard

1569. Number of Ways to Reorder Array to Get Same BST

Kotlin

Count permutations of an array with identical Binary Search Tree

Tree Binary Search Array

binary search tree hash map depth first search recursive relation with memoization counting permutations based on subtree sizes binary search tree

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15.06.2023

medium

1161. Maximum Level Sum of a Binary Tree

Kotlin

Binary Tree level with max sum

Tree

queue binary_tree breadth_first_search level_order_traversal

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14.06.2023

easy

530. Minimum Absolute Difference in BST

Kotlin

Min difference in a BST

Tree

binary-search-tree Morris traversal in-order traversal difference tree

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20.04.2023

medium

662. Maximum Width of Binary Tree

Kotlin

We can do BFS and track node positions.

Graph Tree

ArrayDeque Pair Breadth-First Search Level Order Traversal Level Order Width Calculation Tree

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19.04.2023

medium

1372. Longest ZigZag Path in a Binary Tree

Kotlin

Compute the max as you go

Graph Tree

binary tree depth-first search depth-first search exploring all paths using depth-first search

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17.03.2023

medium

208. Implement Trie (Prefix Tree)

Kotlin

Let's try to write it Kotlin-way

Tree Trie String

Trie Array Strings

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16.03.2023

medium

106. Construct Binary Tree from Inorder and Postorder Traversal

Kotlin

To more robust code, consider moving postTo variable as we go in the reverse-postorder: from the right to the left.

Tree

hash-map recursion index-mapping tree

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15.03.2023

medium

958. Check Completeness of a Binary Tree

Kotlin

Right depth must not be larger than left.

Graph Tree

binary tree depth-first search depth-first search tracking min and max depth

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13.03.2023

easy

101. Symmetric Tree

Kotlin

Recursive: just write helper function.

Graph Tree Stack

ArrayDeque Stack Recursion Breadth-First Search Stack usage for level-order traversal simulation Recursive comparison of mirrored subtrees

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11.03.2023

medium

109. Convert Sorted List to Binary Search Tree

Kotlin

Compute the middle of the linked list.

Tree Binary Search Linked List

ListNode TreeNode recursive_divide_and_conquer divide_and_conquer binary_search_tree linked_list

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28.02.2023

medium

652. Find Duplicate Subtrees

Kotlin

Let's use pre-order traversal and serialize each node into string, also add that into HashSet and check for duplicates.

Tree String

HashSet String DFS Preorder Traversal Serialization Tree

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27.02.2023

medium

427. Construct Quad Tree

Kotlin

use inclusive ranges to simplify the code

Graph Tree Array

Node grid Depth-First Search Divide and Conquer Grid traversal

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19.02.2023

medium

103. Binary Tree Zigzag Level Order Traversal

Kotlin

for zigzag, we can skip a boolean variable and track result count.

Graph Tree

LinkedList ArrayDeque Breadth-First Search Level Order Traversal Zigzag Ordering Binary Tree

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18.02.2023

easy

226. Invert Binary Tree

Kotlin

Let's write a recursive one-liner.

Tree

binary tree implicit recursion depth-first search

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17.02.2023

easy

783. Minimum Distance Between BST Nodes

Kotlin

Let's write Morris Traversal. Store current node at the rightmost end of the left children.

Tree Binary Search Math

Binary Search Tree Linked List Morris Traversal Inorder Traversal for Sequence Rightmost Left Pointer Setup Trees

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16.02.2023

easy

104. Maximum Depth of Binary Tree

Kotlin

Let's write a one-liner.

Graph Tree

binary tree depth-first search recursive depth calculation

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12.01.2023

medium

1519. Number of Nodes in the Sub-Tree With the Same Label

Kotlin

fun countSubTrees(n: Int, edges: Array, labels: String): IntArray {

Graph Tree String

mutableMapOf IntArray DepthFirstSearch use parent instead of visited set in-place counting and subtract count before graph

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11.01.2023

medium

1443. Minimum Time to Collect All Apples in a Tree

Kotlin

fun minTime(n: Int, edges: Array, hasApple: List): Int {

Graph Tree Queue

graph array queue depth-first-search breadth-first-search cycle-handling

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10.01.2023

easy

100. Same Tree

Kotlin

fun isSameTree(p: TreeNode?, q: TreeNode?): Boolean = p == null && q == null ||

Tree Stack

TreeNode recursive traversal recursive comparison of tree structures

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9.01.2023

easy

144. Binary Tree Preorder Traversal

Kotlin

class Solution {

Tree

mutableListOf ArrayDeque preorder_traversal_rec preorder_traversal_stack Morris's algorithm binary_tree

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22.12.2022

hard

834. Sum of Distances in Tree

Kotlin

fun sumOfDistancesInTree(n: Int, edges: Array): IntArray {

Graph Tree Array

mutableMapOf IntArray depth-first-search dfs reusing-results sum[curr] = sum[prev] - count[curr] + (N - count[curr])

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11.12.2022

hard

124. Binary Tree Maximum Path Sum

Kotlin

fun maxPathSum(root: TreeNode?): Int {

Graph Tree

binary tree pair depth-first search recursion dynamic programming arrays

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10.12.2022

medium

1339. Maximum Product of Splitted Binary Tree

Kotlin

fun maxProduct(root: TreeNode?): Int {

Graph Tree

binary_tree pair depth_first_search dp prefix_sum arithmetic

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7.12.2022

easy

938. Range Sum of BST

Kotlin

fun rangeSumBST(root: TreeNode?, low: Int, high: Int): Int =

Tree

binary search tree recursion bst traversal tree arrays

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15.11.2022

medium

Count Complete Tree Nodes

Kotlin

x

Tree

TreeNode none recursion logarithmic-depth-check tree-height-comparison

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Tree

100 entries