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| 1 | +# Problem: Check If a Prerequisite Exists |
| 2 | + |
| 3 | +This repository provides solutions to the problem "Check If a Prerequisite Exists" implemented in **C++**, **Java**, **JavaScript**, **Python**, and **Go**. Below, you'll find step-by-step explanations for each language. |
| 4 | + |
| 5 | +--- |
| 6 | + |
| 7 | +## C++ Code Implementation: Step-by-Step |
| 8 | + |
| 9 | +1. **Initialize the Adjacency Matrix** |
| 10 | + Start by initializing a 2D matrix to store whether a course is a prerequisite of another course. |
| 11 | + |
| 12 | +2. **Set up the Prerequisite Relationships** |
| 13 | + Using the prerequisites list, update the adjacency matrix with direct relationships between courses. |
| 14 | + |
| 15 | +3. **Floyd-Warshall Algorithm** |
| 16 | + Apply the Floyd-Warshall algorithm to compute all pairs' reachability. This updates the matrix to reflect indirect prerequisites. |
| 17 | + |
| 18 | +4. **Process the Queries** |
| 19 | + For each query, check the adjacency matrix to see if one course is a prerequisite of another. |
| 20 | + |
| 21 | +--- |
| 22 | + |
| 23 | +## Java Code Implementation: Step-by-Step |
| 24 | + |
| 25 | +1. **Prepare the Adjacency Matrix** |
| 26 | + Create a 2D array to store whether a course is a prerequisite for another. |
| 27 | + |
| 28 | +2. **Update Relationships from Prerequisites** |
| 29 | + Populate the matrix with the prerequisites directly given in the input. |
| 30 | + |
| 31 | +3. **Use Floyd-Warshall Algorithm** |
| 32 | + Implement Floyd-Warshall to ensure all transitive prerequisites are captured in the matrix. |
| 33 | + |
| 34 | +4. **Answer the Queries** |
| 35 | + For each query, use the matrix to determine if the prerequisite relationship exists. |
| 36 | + |
| 37 | +--- |
| 38 | + |
| 39 | +## JavaScript Code Implementation: Step-by-Step |
| 40 | + |
| 41 | +1. **Build the Graph** |
| 42 | + Create a graph representation using a 2D array to represent the prerequisite relationships. |
| 43 | + |
| 44 | +2. **Populate Direct Relationships** |
| 45 | + Populate the graph with direct prerequisites using the input data. |
| 46 | + |
| 47 | +3. **Compute Transitive Closure** |
| 48 | + Utilize the Floyd-Warshall algorithm to compute transitive relationships between courses. |
| 49 | + |
| 50 | +4. **Evaluate Queries** |
| 51 | + Loop through each query and return whether the course relationship exists. |
| 52 | + |
| 53 | +--- |
| 54 | + |
| 55 | +## Python Code Implementation: Step-by-Step |
| 56 | + |
| 57 | +1. **Initialize a 2D Matrix** |
| 58 | + Create a matrix where `matrix[i][j]` indicates whether course `i` is a prerequisite for course `j`. |
| 59 | + |
| 60 | +2. **Update the Matrix for Direct Prerequisites** |
| 61 | + Populate the matrix with the relationships provided in the prerequisites list. |
| 62 | + |
| 63 | +3. **Apply Floyd-Warshall Algorithm** |
| 64 | + Implement the Floyd-Warshall algorithm to find all indirect relationships between courses. |
| 65 | + |
| 66 | +4. **Answer the Queries** |
| 67 | + For each query, check the value in the matrix to determine if the prerequisite exists. |
| 68 | + |
| 69 | +--- |
| 70 | + |
| 71 | +## Go Code Implementation: Step-by-Step |
| 72 | + |
| 73 | +1. **Set up the Graph as a 2D Slice** |
| 74 | + Initialize a 2D slice to represent the adjacency matrix of course relationships. |
| 75 | + |
| 76 | +2. **Add Direct Relationships** |
| 77 | + Update the graph with the direct prerequisites based on the input data. |
| 78 | + |
| 79 | +3. **Floyd-Warshall Algorithm for Transitive Closure** |
| 80 | + Implement Floyd-Warshall to propagate indirect prerequisites across the matrix. |
| 81 | + |
| 82 | +4. **Handle Queries** |
| 83 | + For each query, determine whether a course is a prerequisite by checking the matrix. |
| 84 | + |
| 85 | +--- |
| 86 | + |
| 87 | +Each implementation shares a common approach: |
| 88 | + |
| 89 | +1. Build a representation of prerequisites. |
| 90 | +2. Compute all transitive relationships using the Floyd-Warshall algorithm. |
| 91 | +3. Check the matrix to answer queries. |
| 92 | + |
| 93 | +For the complete implementation, refer to the respective files: |
| 94 | + |
| 95 | +- `solution.cpp` |
| 96 | +- `solution.java` |
| 97 | +- `solution.js` |
| 98 | +- `solution.py` |
| 99 | +- `solution.go` |
| 100 | + |
| 101 | +--- |
| 102 | + |
| 103 | +### Complexity Analysis |
| 104 | + |
| 105 | +- **Time Complexity**: |
| 106 | + The Floyd-Warshall algorithm takes $$O(n^3)$$ time, where \(n\) is the number of courses. Processing the queries takes $$O(q)$$, where \(q\) is the number of queries. |
| 107 | + |
| 108 | +- **Space Complexity**: |
| 109 | + The space complexity is $$O(n^2)$$ for the adjacency matrix. |
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