2025-01-27 Daily Challenge

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In: DailyChallenge

Today I have done leetcode's January LeetCoding Challenge with cpp.

January LeetCoding Challenge 27

Description

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.

 

Example 1:

Input: numCourses = 2, prerequisites = [[1,0]], queries = [[0,1],[1,0]]
Output: [false,true]
Explanation: The pair [1, 0] indicates that you have to take course 1 before you can take course 0.
Course 0 is not a prerequisite of course 1, but the opposite is true.

Example 2:

Input: numCourses = 2, prerequisites = [], queries = [[1,0],[0,1]]
Output: [false,false]
Explanation: There are no prerequisites, and each course is independent.

Example 3:

Input: numCourses = 3, prerequisites = [[1,2],[1,0],[2,0]], queries = [[1,0],[1,2]]
Output: [true,true]

 

Constraints:

  • 2 <= numCourses <= 100
  • 0 <= prerequisites.length <= (numCourses * (numCourses - 1) / 2)
  • prerequisites[i].length == 2
  • 0 <= ai, bi <= numCourses - 1
  • ai != bi
  • All the pairs [ai, bi] are unique.
  • The prerequisites graph has no cycles.
  • 1 <= queries.length <= 104
  • 0 <= ui, vi <= numCourses - 1
  • ui != vi

Solution

class Solution {
public:
  vector<bool> checkIfPrerequisite(int n, vector<vector<int>>& prerequisites, vector<vector<int>>& queries) {
    vector<vector<bool>> isPrerequisite(n, vector<bool>(n));
    for(auto &pre : prerequisites) {
      isPrerequisite[pre[0]][pre[1]] = true;
    }
    
    for(int k = 0; k < n; ++k) {
      for(int i = 0; i < n; ++i) {
        for(int j = 0; j < n; ++j) {
          if(isPrerequisite[i][k] && isPrerequisite[k][j]) {
            isPrerequisite[i][j] = true;
          }
        }
      }
    }
    
    vector<bool> answer;
    for(auto &query : queries) {
      answer.push_back(isPrerequisite[query[0]][query[1]]);
    }
    return answer;
  }
};

// Accepted
// 69/69 cases passed (55 ms)
// Your runtime beats 54.36 % of cpp submissions
// Your memory usage beats 96.16 % of cpp submissions (63.8 MB)
Algorithm