5699. Number of Restricted Paths From First to Last Node  Summary and Q&A
TL;DR
The video explains how to find restricted paths in a weighted graph.
Key Insights
 🏋️ Understanding the concept of restricted paths is vital in graph theory in relation to the specific adjacency and weight conditions.
 🍰 Implementing Dijkstra's algorithm is crucial for determining the shortest distances required to establish valid descending routes in a weighted graph.
 ✅ The combination of DFS and dynamic programming not only simplifies the pathfinding process but also enhances computational efficiency by avoiding redundant checks.
 The graphical representation and practical examples provided can aid viewers in grasping the complexities involved in solving graphrelated problems algorithmically.
 🏋️ Clarifying the indications of node connections and their associated weights is a necessary step in effectively navigating through the restrictions posed by the problem.
 👨💻 Regular updates to the video series show the evolving complexity of coding interview preparation, highlighting essential algorithms and problemsolving strategies.
 🫒 Engaging with community resources like Telegram channels for live doubt sessions fosters collaborative learning and offers immediate support for complex topics.
Transcript
hi everyone welcome back to lead coding so in this video we are discussing the third problem of the lead code weekly contest 231 name of the problem is number of restricted paths from first to last node now there is an undirected weighted connected graph you are given a positive integer n where n denotes the total number of nodes labeled from 1 to ... Read More
Questions & Answers
Q: What is meant by a "restricted path" in the context of this problem?
A restricted path is defined as a sequence of nodes in which the distance to the last node diminishes as we progress through the path. Each node's distance to the last node must be greater than the subsequent node's distance in the sequence, ensuring a strictly decreasing pattern in values.
Q: How does Dijkstra's algorithm apply to this problem?
Dijkstra's algorithm is utilized to compute the shortest distances from the last node to every other node in the graph. This is essential because these distances determine which paths can be considered valid under the restriction that each path must descend in distance, thereby informing the conditions necessary for traversing from the start node to the end node.
Q: Why is dynamic programming used alongside DFS in this scenario?
Dynamic programming is integrated with depthfirst search to optimize the process of pathfinding by caching results of previously computed paths. This helps in avoiding repetitive calculations when revisiting nodes, ultimately improving efficiency and enabling the tracking of the number of unique paths that meet the required distance conditions.
Q: How does one implement the depthfirst search in this problem?
The depthfirst search is conducted by starting from the initial node and recursively exploring connected nodes. While traversing to children nodes, the algorithm checks whether their distance values meet the restriction of being less than their parent’s value. Valid paths are counted and returned, accumulating the total number of allowable routes as the search progresses.
Summary & Key Takeaways

The content introduces the problem of finding restricted paths in an undirected weighted graph, explaining the rules and requirements for paths that must have decreasing distances to the last node.

It highlights the application of Dijkstra’s algorithm to calculate the shortest distances from the last node to all others, which is fundamental for determining valid paths based on specific conditions.

The analysis emphasizes the use of depthfirst search (DFS) combined with dynamic programming to efficiently explore all possible paths while avoiding repetitive calculations.