https://github.com/emahtab/course-schedule-iv

https://github.com/emahtab/course-schedule-iv

floyd-warshall-algorithm graph leetcode

Last synced: 3 months ago
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• Host: GitHub
• URL: https://github.com/emahtab/course-schedule-iv
• Owner: eMahtab
• Created: 2021-12-24T16:46:33.000Z (over 3 years ago)
• Default Branch: main
• Last Pushed: 2022-01-03T02:09:00.000Z (over 3 years ago)
• Last Synced: 2025-02-02T03:26:03.556Z (5 months ago)
• Topics: floyd-warshall-algorithm, graph, leetcode
• Homepage:
• Size: 49.8 KB
• Stars: 1
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
# Course Schedule IV

## https://leetcode.com/problems/course-schedule-iv

There are a total of numCourses courses you have to take, labeled from 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [ai, bi] indicates that you must take course ai first if you want to take course bi.

For example, the pair [0, 1] indicates that you have to take course 0 before you can take course 1.

**Prerequisites can also be indirect. If course a is a prerequisite of course b, and course b is a prerequisite of course c, then course a is a prerequisite of course c.**

You are also given an array queries where queries[j] = [uj, vj]. For the jth query, you should answer whether course uj is a prerequisite of course vj or not.

Return a boolean array answer, where answer[j] is the answer to the jth query.

![Course Schedule IV](example.JPG?raw=true)

# Implementation : Floyd Warshall Algorithm O(n^3)

```java

class Solution {

    public List checkIfPrerequisite(int n, int[][] prerequisites, int[][] queries) {

        boolean[][] connected = new boolean[n][n];

        for (int[] p : prerequisites)

            connected[p[0]][p[1]] = true; // p[0] -> p[1]

        for (int k = 0; k < n; k++)

            for (int i = 0; i < n; i++)

                for (int j = 0; j < n; j++)

                    connected[i][j] = connected[i][j] || connected[i][k] && connected[k][j];

        List result = new ArrayList<>();

        for (int[] q : queries)

            result.add(connected[q[0]][q[1]]);

        return result;

    }

}

```

# References :

https://www.youtube.com/watch?v=oNI0rf2P9gE (Abdul Bari, Floyd Warshall : All Pairs Shortest Path Algorithm)

https://leetcode.com/problems/course-schedule-iv/discuss/660509/JavaPython-FloydWarshall-Algorithm-Clean-code-O(n3)