Memoization LeetCode Problems: 39 Python Solutions

1 pattern

How Memoization problems are solved

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

Dynamic ProgrammingDefine a state, write the transition, and stop recomputing the same subproblem.

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When the Memoization problem arrives live.

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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...

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Memoization problems by difficulty

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

Easy (3)

Easy problems
No.	Problem	Topics
0070	Climbing Stairs	Memoization, Math, Dynamic Programming
0509	Fibonacci Number	Recursion, Memoization, Math +1
1137	N-th Tribonacci Number	Memoization, Math, Dynamic Programming

Medium (11)

Medium problems
No.	Problem	Topics
0139	Word Break	Trie, Memoization, Array +3
0241	Different Ways to Add Parentheses	Recursion, Memoization, Math +2
0397	Integer Replacement	Greedy, Bit Manipulation, Memoization +1
0464	Can I Win	Bit Manipulation, Memoization, Math +3
0638	Shopping Offers	Bit Manipulation, Memoization, Array +3
0698	Partition to K Equal Sum Subsets	Bit Manipulation, Memoization, Array +3
0894	All Possible Full Binary Trees	Tree, Recursion, Memoization +2
1387	Sort Integers by The Power Value	Memoization, Dynamic Programming, Sorting
2311	Longest Binary Subsequence Less Than or Equal to K	Greedy, Memoization, String +1
2998	Minimum Number of Operations to Make X and Y Equal	Breadth-First Search, Memoization, Dynamic Programming
0294	Flip Game IIPremium	Memoization, Math, Dynamic Programming +2

Hard (25)

Hard problems
No.	Problem	Topics
0140	Word Break II	Trie, Memoization, Array +4
0329	Longest Increasing Path in a Matrix	Depth-First Search, Breadth-First Search, Graph +5
0488	Zuma Game	Stack, Breadth-First Search, Memoization +2
0546	Remove Boxes	Memoization, Array, Dynamic Programming
0691	Stickers to Spell Word	Bit Manipulation, Memoization, Array +5
0773	Sliding Puzzle	Breadth-First Search, Memoization, Array +3
0913	Cat and Mouse	Graph, Topological Sort, Memoization +3
0964	Least Operators to Express Number	Memoization, Math, Dynamic Programming
1444	Number of Ways of Cutting a Pizza	Memoization, Array, Dynamic Programming +2
1553	Minimum Number of Days to Eat N Oranges	Memoization, Dynamic Programming
1569	Number of Ways to Reorder Array to Get Same BST	Tree, Union Find, Binary Search Tree +7
1575	Count All Possible Routes	Memoization, Array, Dynamic Programming
1611	Minimum One Bit Operations to Make Integers Zero	Bit Manipulation, Memoization, Dynamic Programming
1659	Maximize Grid Happiness	Bit Manipulation, Memoization, Dynamic Programming +1
1728	Cat and Mouse II	Graph, Topological Sort, Memoization +5
1815	Maximum Number of Groups Getting Fresh Donuts	Bit Manipulation, Memoization, Array +2
1857	Largest Color Value in a Directed Graph	Graph, Topological Sort, Memoization +3
1900	The Earliest and Latest Rounds Where Players Compete	Memoization, Dynamic Programming
2019	The Score of Students Solving Math Expression	Stack, Memoization, Array +4
2312	Selling Pieces of Wood	Memoization, Array, Dynamic Programming
2318	Number of Distinct Roll Sequences	Memoization, Dynamic Programming
2328	Number of Increasing Paths in a Grid	Depth-First Search, Breadth-First Search, Graph +5
2713	Maximum Strictly Increasing Cells in a Matrix	Memoization, Array, Hash Table +5
2876	Count Visited Nodes in a Directed Graph	Graph, Memoization, Dynamic Programming
2920	Maximum Points After Collecting Coins From All Nodes	Bit Manipulation, Tree, Depth-First Search +3

Memoization LeetCode Problems: All 39,
With Python Solutions

How Memoization problems are solved

When the Memoization problem arrives live.

Approach

Approach

Approach

Memoization problems by difficulty

Easy (3)

Medium (11)

Hard (25)

Keep exploring

How Memoization problems are solved

When the Memoization problem arrives live.

Approach

Approach

Approach

Memoization problems by difficulty

Easy (3)3

Medium (11)11

Hard (25)25

Keep exploring

Easy (3)

Medium (11)

Hard (25)