Divide and Conquer LeetCode Problems: All 47,
With Python Solutions

Every problem in this library that LeetCode tags Divide and Conquer. 41 of them carry a complete Python solution, a worked example and the time and space complexity of the approach.

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Easy: 5
Medium: 26
Hard: 16

Divide and Conquer problems by difficulty

Problems with a complete Python solution are listed first, then by ascending problem number.

Easy (5)

Easy problems
No.	Problem	Topics
0108	Convert Sorted Array to Binary Search Tree	Tree, Binary Search Tree, Array +2
0169	Majority Element	Array, Hash Table, Divide and Conquer +2
0190	Reverse Bits	Bit Manipulation, Divide and Conquer
0191	Number of 1 Bits	Bit Manipulation, Divide and Conquer
1763	Longest Nice Substring	Bit Manipulation, Hash Table, String +2

Medium (26)

Medium problems
No.	Problem	Topics
0053	Maximum Subarray	Array, Divide and Conquer, Dynamic Programming
0105	Construct Binary Tree from Preorder and Inorder Traversal	Tree, Array, Hash Table +2
0106	Construct Binary Tree from Inorder and Postorder Traversal	Tree, Array, Hash Table +2
0109	Convert Sorted List to Binary Search Tree	Tree, Binary Search Tree, Linked List +2
0148	Sort List	Linked List, Two Pointers, Divide and Conquer +2
0215	Kth Largest Element in an Array	Array, Divide and Conquer, Quickselect +2
0240	Search a 2D Matrix II	Array, Binary Search, Divide and Conquer +1
0307	Range Sum Query - Mutable	Design, Binary Indexed Tree, Segment Tree +2
0324	Wiggle Sort II	Greedy, Array, Divide and Conquer +2
0347	Top K Frequent Elements	Array, Hash Table, Divide and Conquer +5
0372	Super Pow	Math, Divide and Conquer
0395	Longest Substring with At Least K Repeating Characters	Hash Table, String, Divide and Conquer +1
0427	Construct Quad Tree	Tree, Array, Divide and Conquer +1
0558	Logical OR of Two Binary Grids Represented as Quad-Trees	Tree, Divide and Conquer
0654	Maximum Binary Tree	Stack, Tree, Array +3
0889	Construct Binary Tree from Preorder and Postorder Traversal	Tree, Array, Hash Table +2
0912	Sort an Array	Array, Divide and Conquer, Bucket Sort +5
0918	Maximum Sum Circular Subarray	Queue, Array, Divide and Conquer +2
0932	Beautiful Array	Array, Math, Divide and Conquer
0973	K Closest Points to Origin	Geometry, Array, Math +4
1382	Balance a Binary Search Tree	Greedy, Tree, Depth-First Search +3
1738	Find Kth Largest XOR Coordinate Value	Bit Manipulation, Array, Divide and Conquer +5
1985	Find the Kth Largest Integer in the Array	Array, String, Divide and Conquer +3
2343	Query Kth Smallest Trimmed Number	Array, String, Divide and Conquer +4
1756	Design Most Recently Used QueuePremium	Design, Array, Linked List +3
2031	Count Subarrays With More Ones Than ZerosPremium	Binary Indexed Tree, Segment Tree, Array +5

Hard (16)

Hard problems
No.	Problem	Topics
0004	Median of Two Sorted Arrays	Array, Binary Search, Divide and Conquer
0023	Merge k Sorted Lists	Linked List, Divide and Conquer, Heap (Priority Queue) +1
0218	The Skyline Problem	Binary Indexed Tree, Segment Tree, Array +5
0315	Count of Smaller Numbers After Self	Binary Indexed Tree, Segment Tree, Array +4
0327	Count of Range Sum	Binary Indexed Tree, Segment Tree, Array +4
0493	Reverse Pairs	Binary Indexed Tree, Segment Tree, Array +4
1569	Number of Ways to Reorder Array to Get Same BST	Tree, Union Find, Binary Search Tree +7
1649	Create Sorted Array through Instructions	Binary Indexed Tree, Segment Tree, Array +4
1982	Find Array Given Subset Sums	Array, Divide and Conquer
2179	Count Good Triplets in an Array	Binary Indexed Tree, Segment Tree, Array +4
2407	Longest Increasing Subsequence II	Binary Indexed Tree, Segment Tree, Queue +4
2426	Number of Pairs Satisfying Inequality	Binary Indexed Tree, Segment Tree, Array +4
1274	Number of Ships in a RectanglePremium	Array, Divide and Conquer, Interactive
2519	Count the Number of K-Big IndicesPremium	Binary Indexed Tree, Segment Tree, Array +4
2613	Beautiful PairsPremium	Geometry, Array, Math +3
2792	Count Nodes That Are Great EnoughPremium	Tree, Depth-First Search, Divide and Conquer +1

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python

Please analyze this context and help me answer the question or solve the problem.

Technical interview · 45 minsolution.pyShared editor · Python 3Longest substring without repeatsMediumGiven a string s, return the length of the longest contiguous substring in which every character is unique.s = "abcabcbb"
→ 31def length_of_longest_substring(s: str) -> int:2 last_seen = {}3 left = best = 04 for right, ch in enumerate(s):5 if ch in last_seen and last_seen[ch] >= left:

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

Type your message...

GPT-6.1 Terra

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python

Please analyze this context and help me answer the question or solve the problem.

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

Type your message...

GPT-6.1 TerraClear chat

QuitEscHide+QCapture+PCrop+OSubmit+EnterPress to get answerLeft/Right+Up/Down+

90%Subscription

python

Please analyze this context and help me answer the question or solve the problem.

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

Type your message...

GPT-6.1 TerraClear chat

Primary display

QuitEscHide+QCapture+PCrop+OSubmit+EnterPress to get answerLeft/Right+Up/Down+

Divide and Conquer problems by difficulty

Easy (5)5

Medium (26)26

Hard (16)16

When the Divide and Conquer problem arrives live.

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Easy (5)

Medium (26)

Hard (16)