Topological Sort LeetCode Problems: 32 Python Solutions

1 pattern

How Topological Sort problems are solved

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

Topological SortOrder a set of tasks so that every dependency comes before the thing that needs it.

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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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Topological Sort problems by difficulty

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

Medium (14)

Medium problems
No.	Problem	Topics
0207	Course Schedule	Depth-First Search, Breadth-First Search, Graph +1
0210	Course Schedule II	Depth-First Search, Breadth-First Search, Graph +1
0310	Minimum Height Trees	Depth-First Search, Breadth-First Search, Graph +1
0802	Find Eventual Safe States	Depth-First Search, Breadth-First Search, Graph +1
0851	Loud and Rich	Depth-First Search, Graph, Topological Sort +1
1462	Course Schedule IV	Depth-First Search, Breadth-First Search, Graph +1
1786	Number of Restricted Paths From First to Last Node	Graph, Topological Sort, Dynamic Programming +2
1976	Number of Ways to Arrive at Destination	Graph, Topological Sort, Dynamic Programming +1
2115	Find All Possible Recipes from Given Supplies	Graph, Topological Sort, Array +2
2192	All Ancestors of a Node in a Directed Acyclic Graph	Depth-First Search, Breadth-First Search, Graph +1
0444	Sequence ReconstructionPremium	Graph, Topological Sort, Array
1059	All Paths from Source Lead to DestinationPremium	Graph, Topological Sort
1136	Parallel CoursesPremium	Graph, Topological Sort
1245	Tree DiameterPremium	Tree, Depth-First Search, Breadth-First Search +2

Hard (18)

Hard problems
No.	Problem	Topics
0329	Longest Increasing Path in a Matrix	Depth-First Search, Breadth-First Search, Graph +5
0913	Cat and Mouse	Graph, Topological Sort, Memoization +3
1203	Sort Items by Groups Respecting Dependencies	Depth-First Search, Breadth-First Search, Graph +1
1632	Rank Transform of a Matrix	Union Find, Graph, Topological Sort +3
1728	Cat and Mouse II	Graph, Topological Sort, Memoization +5
1857	Largest Color Value in a Directed Graph	Graph, Topological Sort, Memoization +3
1916	Count Ways to Build Rooms in an Ant Colony	Tree, Graph, Topological Sort +3
2050	Parallel Courses III	Graph, Topological Sort, Array +1
2127	Maximum Employees to Be Invited to a Meeting	Depth-First Search, Graph, Topological Sort
2246	Longest Path With Different Adjacent Characters	Tree, Depth-First Search, Graph +3
2328	Number of Increasing Paths in a Grid	Depth-First Search, Breadth-First Search, Graph +5
2360	Longest Cycle in a Graph	Depth-First Search, Breadth-First Search, Graph +1
2392	Build a Matrix With Conditions	Graph, Topological Sort, Array +1
2603	Collect Coins in a Tree	Tree, Graph, Topological Sort +1
0269	Alien DictionaryPremium	Depth-First Search, Breadth-First Search, Graph +3
0631	Design Excel Sum FormulaPremium	Graph, Design, Topological Sort +4
1591	Strange Printer II	Graph, Topological Sort, Array +1
2371	Minimize Maximum Value in a GridPremium	Union Find, Graph, Topological Sort +3

Topological Sort LeetCode Problems: All 32,
With Python Solutions

How Topological Sort problems are solved

When the Topological Sort problem arrives live.

Approach

Approach

Approach

Topological Sort problems by difficulty

Medium (14)

Hard (18)

Keep exploring

How Topological Sort problems are solved

When the Topological Sort problem arrives live.

Approach

Approach

Approach

Topological Sort problems by difficulty

Medium (14)14

Hard (18)18

Keep exploring

Medium (14)

Hard (18)