round trip cses usaco

[Video Tutorial Series] Graph Theory: From Beginner to Intermediate - Dardev

I am planning to post all solutions of CSES graph series ; while also discussing the necessary theory involved.

Update: I reuploaded the first 12 videos with better audio quality . All audios are good now.

Here is the entire playlist: Graph Theory Introduction Part 1 :: Overview and Representations of Graph - YouTube

Intro part 1: Graph Theory Introduction Part 1 :: Overview and Representations of Graph - YouTube

Intro part 2: Graph Theory Introduction Part 2 :: DFS and BFS - YouTube

CSES 1: Counting Rooms(1192): Graph 01: Counting Rooms (CSES 1192) :: Graph Theory: Flood Fill, DFS on a Grid, CSES 01 - YouTube

CSES 2: Labyrinth(1193): Graph 06: Labyrinth:: BFS on a Grid (CSES Graph 02: 1193) - YouTube

CSES 3: Building Roads: Graph 02: Building Roads :: Min Cost to Connect Graph with Unweighted Edges. (CSES Graph 03: 1666) - YouTube

CSES 4: Message Route Graph 05: Message Route :: BFS in Undirected. Single Source Shortest Path. (CSES Graph 04: 1667) - YouTube

CSES 5: Building Teams: Graph 03: Building Teams :: Graph Theory: Bipartite Graph, 2 Color Problem, CSES Graphs 05: 1668 - YouTube

CSES 6: Round Trip: Graph 04: Round Trip :: Cycle Retrieval, Cycle Detection, Undirected Graph, CSES 06: 1669 - YouTube

CSES 7: Monsters: Graph 07: Monsters :: Lava Flow, Multi-source BFS, BFS on a Grid (CSES 07: 1194) - YouTube

Theory Time: Heaps Part 1 — Intro to Heaps, Trees, Rooting a Tree, Binary Tree, Complete Binary Tree Graph 8.1: Heaps 1:: Intro to Heaps, Trees, Rooting a Tree, Binary Tree, Complete Binary Tree - YouTube

Theory Time: Heaps Part 2 — Inserting, Retrieving, Heapfication into Heap Graph 8.2: Heaps 2:: Inserting into, Retrieving from a Binary Min Heap. Heapfication. - YouTube

Theory Time: Heaps Part 3 — Flattening Heap into Vector. Navigating a Flattened Tree Graph 8.3: Heaps 3:: Flattening Heap into Vector. Navigating a Flattened Tree - YouTube

CSES 8: Shortest Routes I: 09 Graph Theory:: Dijkstra's Algorithm with CSES 08 Shortest Routes I (1671) - YouTube

CSES 9: Shortest Routes II: 11 Graph Theory:: Floyd Warshalls with CSES 9 Shortest Routes II (1672) All Source Shortest Paths - YouTube

CSES 10: High Score: 10 Graph Theory:: Bellman Ford's Algorithm with CSES 10 High Score (1673) - YouTube

CSES 11: Flight Discount: 12 Graph Theory:: Dijkstras with CSES 11 Flight Discount (1195) Single Source Shortest Path Modified - YouTube

CSES 12: Cycle Finding: 14 Graph Theory:: Bellman-Ford with CSES 12 Cycle Finding (1197) Retrieve Negative Cycle - YouTube

CSES 13: Flight Routes: 13 Graph Theory:: Dijkstras with CSES 13 Flight Routes (1196) Single Source Shortest PathS Modified - YouTube

CSES 14: Round Trip II: 15 Graph Theory:: DFS with Stack to Retrieve Cycle in Directed Graph CSES Round Trip II 1678 - YouTube

CSES 15: Course Schedule: 16 Graph Theory:: Topological Sort with CSES: Course Schedule 1679 - YouTube

CSES 16: Longest Flight Route: Graph 17: Longest Flight Route :: Modified Dijkstras(CSES 16: 1680) - YouTube

CSES 17: Game Routes: Graph 19: Game Routes:: Topological Sorting(CSES 17: 1681) - YouTube

CSES 18: Investigation: Graph 18: Investigation:: Modified Dijkstras(CSES 18: 1202) - YouTube

CSES 19: Planet Queries I

Planet Queries II

Very underrated. Your explanations are amazing!

I liked how you submitted your single source BFS code to prove that it won’t work.

Thanks! I am glad you are following the series.

Here are the updates:

I solved another CSES problem: Lava Flow and Multisource BFS - YouTube

Introduction to Trees, Binary Trees, Min/Max Heaps, Flattening a Tree into a Vector - YouTube

I made an introductory video 00 to make things even simpler - YouTube

I am reuploading the solution to the first problem, for greater audio clarity and better explanation/presentation - YouTube

Today I will try and share Dijkstra theory while solving the next CSES problem.

Language dependent or independent videos ?

I explain concepts in English. But my implementation is in C++, I explain every critical aspect of code though. Just check it out, you’ll like it.

This video series is really helpful! I am really excited about this series and will keep posting updates to support you. I just finished the first two videos. Nice explanation of BFS and DFS on the grid.

Thanks a lot for you effort and hard work. It is really helpful for the coding comminity.

Thank you guys. Please subscribe! Its a humble request . Will post more videos soon.

Hey please try to make a few more videos on Dijkstra algo, with some interesting problems

Done with Dijkstra:: 09 Graph Theory:: Dijkstra's Algorithm with CSES 08 Shortest Routes I (1671) - YouTube

Do give feedback, please!

I will be adding Bellman-Ford and solving more problems starting tomorrow.

Please keep following this series to improve your understanding of graph theory.

Hey, can you help me with this problem?

Check out my DFS

See what i did there? I created a global vector idx and did the following to track the edge being currently explored.

When I come back, I don’t start checking ALL neighbours of vertex ‘u’. I simply continue from where I left. Hope that makes sense?

If we don’t take care of this, we will search ALL edges every time in the following case. I am calling this graph a flower-with-petal graph. Only seven petals in this graph, but imagine what happens if there are 10^5 petals (with O(N^2) complexity)

If it doesn’t I am not going to type out more here. I try to make a Eulerian Circuit video on priority and explain this aspect clearly.

Watch out for this video series: - YouTube

Hey guys! Just solved another problem for you guys: High Score and this time we study the “Bellman-Ford” Algorithm.

Hope you’ll love it.

one of the best graph theory tutorial is by Code N Code

CSES Problem Set

Round trip ii.

• Time limit: 1.00 s
• Memory limit: 512 MB

Byteland has n cities and m flight connections. Your task is to design a round trip that begins in a city, goes through one or more other cities, and finally returns to the starting city. Every intermediate city on the route has to be distinct.

The first input line has two integers n and m : the number of cities and flights. The cities are numbered 1,2,\dots,n .

Then, there are m lines describing the flights. Each line has two integers a and b : there is a flight connection from city a to city b . All connections are one-way flights from a city to another city.

First print an integer k : the number of cities on the route. Then print k cities in the order they will be visited. You can print any valid solution.

If there are no solutions, print "IMPOSSIBLE".

Constraints

• 1 \le n \le 10^5
• 1 \le m \le 2 \cdot 10^5
• 1 \le a,b \le n

Graph Algorithms

Learn Data Structures and Algorithms

Round Trip (CSES)

Problem link: https://cses.fi/problemset/task/1669

Problem statement: Byteland has n cities and m roads between them. Your task is to design a round trip that begins in a city, goes through two or more other cities, and finally returns to the starting city. Every intermediate city on the route has to be distinct.

The first input line has two integers n and m : the number of cities and roads. The cities are numbered 1,2,…,n. Then, there are m lines describing the roads. Each line has two integers a and b : there is a road between those cities. Every road is between two different cities, and there is at most one road between any two cities.

First print an integer k: the number of cities on the route. Then print k cities in the order they will be visited. You can print any valid solution. If there are no solutions, print “IMPOSSIBLE”.

In the given input format the graph will look like

Here we need to find out the cycle in the graph if the cycle is not exit then we need to return word IMPOSSIBLE and if there is cycle we need to print the length of the cycle and also print the cycle

So First We need to find out the cycle , but how?? To find cycle we need to traverse graph so lets take it as dfs and now while traversing if the upcomming child is visited then there are only two things that’s possible one is it can be a parent , but if it is not a parent then it will be aldready visted then this makes it as a cycle

If you do not know how to find out whether there is cycle print cycle you can go learn from this following blog Cycle_Detection_in_Graphs and try to solve the both practise problems

Related Post

Number of good paths (leetcode).

Greatest Common Divisor Traversal (Leetcode)

Bricks falling when hit (leetcode), 2 thoughts on “round trip (cses)”.

[…] CESS-Round Trip […]

[…] you have understood above concept . then try this famous problemCESS-Round Trip – In this problem you need to find out the cycle in undirected graph and print the […]

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Segment Trees

Dfs in trees, dp on trees.

USACO Forum

Cses nested ranges count.

I am trying to solve this problem from CSES problem set and I’ve not been able to come up even with a half decent idea after spending around 2 hours on it.

I tried to google and read AC’ed solutions but can’t comprehend the approach taken.

Can someone just describe their approach?

let a range be called (start, end)

if we sort the ranges by their start , we can find the number of ranges that contain x by querying the number of ranges y that satisfy y.start \leq x.start and y.end \geq x.end . This fits our situation because if we sort the ranges, then we guarantee that y.start \leq x.start must be true. Thus, we can use a DS like a Binary indexed tree to query the number of ranges that satisfy y.end >= x.end .

counting the number of ranges that x contain is similar.

Thanks a lot for replying.

What does the Binary Indexed Tree store in this case? IIRC, I can query a BIT to get sum of elements in a subarray defined by indexs i and j or update and element at index i , both these operation can be done in \mathcal{O(\log n)} using BIT.

The code that you provided what is BIT storing?

BIT stores the # of ranges

count[x] = BIT.query(x.end, INF) is querying the number of ranges before x that satisfy y.end>=x.end .

BIT.add(x.end, 1); increments that counter for x

Thanks a lot. I got the gist of your approach finally but I ended up solving it using pbds ordered set(a slight modification to use it as ordered multiset)

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