Monotonic Stack LeetCode Problems: 58 Python Solutions

1 pattern

How Monotonic Stack problems are solved

A tag names the subject, not the method. These pattern hubs cover the techniques that actually solve Monotonic Stack problems — each one explains the approach, gives a Python template and states its complexity.

Monotonic StackAnswer "what is the next greater element" for every position in one pass.

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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.

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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...

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

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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 TerraClear chat

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

Monotonic Stack problems by difficulty

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

Easy (2)

Easy problems
No.	Problem	Topics
0496	Next Greater Element I	Stack, Array, Hash Table +1
1475	Final Prices With a Special Discount in a Shop	Stack, Array, Monotonic Stack

Medium (35)

Medium problems
No.	Problem	Topics
0316	Remove Duplicate Letters	Stack, Greedy, String +1
0402	Remove K Digits	Stack, Greedy, String +1
0456	132 Pattern	Stack, Array, Binary Search +2
0503	Next Greater Element II	Stack, Array, Monotonic Stack
0581	Shortest Unsorted Continuous Subarray	Stack, Greedy, Array +3
0654	Maximum Binary Tree	Stack, Tree, Array +3
0739	Daily Temperatures	Stack, Array, Monotonic Stack
0769	Max Chunks To Make Sorted	Stack, Greedy, Array +2
0853	Car Fleet	Stack, Array, Sorting +1
0901	Online Stock Span	Stack, Design, Data Stream +1
0907	Sum of Subarray Minimums	Stack, Array, Dynamic Programming +1
0962	Maximum Width Ramp	Stack, Array, Two Pointers +1
1008	Construct Binary Search Tree from Preorder Traversal	Stack, Tree, Binary Search Tree +3
1019	Next Greater Node In Linked List	Stack, Array, Linked List +1
1081	Smallest Subsequence of Distinct Characters	Stack, Greedy, String +1
1124	Longest Well-Performing Interval	Stack, Array, Hash Table +2
1130	Minimum Cost Tree From Leaf Values	Stack, Greedy, Array +2
1504	Count Submatrices With All Ones	Stack, Array, Dynamic Programming +2
1574	Shortest Subarray to be Removed to Make Array Sorted	Stack, Array, Two Pointers +2
1673	Find the Most Competitive Subsequence	Stack, Greedy, Array +1
1856	Maximum Subarray Min-Product	Stack, Array, Prefix Sum +1
1996	The Number of Weak Characters in the Game	Stack, Greedy, Array +2
2104	Sum of Subarray Ranges	Stack, Array, Monotonic Stack
2289	Steps to Make Array Non-decreasing	Stack, Array, Linked List +1
2487	Remove Nodes From Linked List	Stack, Recursion, Linked List +1
2865	Beautiful Towers I	Stack, Array, Monotonic Stack
2866	Beautiful Towers II	Stack, Array, Monotonic Stack
0255	Verify Preorder Sequence in Binary Search TreePremium	Stack, Tree, Binary Search Tree +4
1762	Buildings With an Ocean ViewPremium	Stack, Array, Monotonic Stack
1950	Maximum of Minimum Values in All SubarraysPremium	Stack, Array, Monotonic Stack
2282	Number of People That Can Be Seen in a GridPremium	Stack, Array, Matrix +1
2297	Jump Game VIIIPremium	Stack, Graph, Array +3
2345	Finding the Number of Visible MountainsPremium	Stack, Array, Sorting +1
2832	Maximal Range That Each Element Is Maximum in ItPremium	Stack, Array, Monotonic Stack
2863	Maximum Length of Semi-Decreasing SubarraysPremium	Stack, Array, Sorting +1

Hard (21)

Hard problems
No.	Problem	Topics
0042	Trapping Rain Water	Stack, Array, Two Pointers +2
0084	Largest Rectangle in Histogram	Stack, Array, Monotonic Stack
0085	Maximal Rectangle	Stack, Array, Dynamic Programming +2
0321	Create Maximum Number	Stack, Greedy, Array +2
0768	Max Chunks To Make Sorted II	Stack, Greedy, Array +2
0975	Odd Even Jump	Stack, Array, Dynamic Programming +3
1526	Minimum Number of Increments on Subarrays to Form a Target Array	Stack, Greedy, Array +2
1776	Car Fleet II	Stack, Array, Math +2
1793	Maximum Score of a Good Subarray	Stack, Array, Two Pointers +2
1944	Number of Visible People in a Queue	Stack, Array, Monotonic Stack
2281	Sum of Total Strength of Wizards	Stack, Array, Prefix Sum +1
2334	Subarray With Elements Greater Than Varying Threshold	Stack, Union Find, Array +1
2454	Next Greater Element IV	Stack, Array, Binary Search +3
2617	Minimum Number of Visited Cells in a Grid	Stack, Breadth-First Search, Union Find +5
2736	Maximum Sum Queries	Stack, Binary Indexed Tree, Segment Tree +4
2818	Apply Operations to Maximize Score	Stack, Greedy, Array +4
2940	Find Building Where Alice and Bob Can Meet	Stack, Binary Indexed Tree, Segment Tree +4
2945	Find Maximum Non-decreasing Array Length	Stack, Queue, Array +4
1063	Number of Valid SubarraysPremium	Stack, Array, Monotonic Stack
2030	Smallest K-Length Subsequence With Occurrences of a Letter	Stack, Greedy, String +1
2355	Maximum Number of Books You Can TakePremium	Stack, Array, Dynamic Programming +1

Monotonic Stack LeetCode Problems: All 58,
With Python Solutions

How Monotonic Stack problems are solved

When the Monotonic Stack problem arrives live.

Approach

Approach

Approach

Monotonic Stack problems by difficulty

Easy (2)

Medium (35)

Hard (21)

Keep exploring

How Monotonic Stack problems are solved

When the Monotonic Stack problem arrives live.

Approach

Approach

Approach

Monotonic Stack problems by difficulty

Easy (2)2

Medium (35)35

Hard (21)21

Keep exploring

Easy (2)

Medium (35)

Hard (21)