2023-07-13 Daily Challenge

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In: DailyChallenge

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

July LeetCoding Challenge 13

Description

Course Schedule

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 bi first if you want to take course ai.

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

Return true if you can finish all courses. Otherwise, return false.

 

Example 1:

Input: numCourses = 2, prerequisites = [[1,0]]
Output: true
Explanation: There are a total of 2 courses to take. 
To take course 1 you should have finished course 0. So it is possible.

Example 2:

Input: numCourses = 2, prerequisites = [[1,0],[0,1]]
Output: false
Explanation: There are a total of 2 courses to take. 
To take course 1 you should have finished course 0, and to take course 0 you should also have finished course 1. So it is impossible.

 

Constraints:

  • 1 <= numCourses <= 2000
  • 0 <= prerequisites.length <= 5000
  • prerequisites[i].length == 2
  • 0 <= ai, bi < numCourses
  • All the pairs prerequisites[i] are unique.

Solution

class Solution {
public:
  bool canFinish(int numCourses, vector<vector<int>>& prerequisites) {
    vector<int> degree(numCourses);
    vector<vector<int>> edges(numCourses);
    for(auto &edge : prerequisites) {
      edges[edge[0]].push_back(edge[1]);
      degree[edge[1]] += 1;
    }
    queue<int> q;
    int answer = 0;
    for(int i = 0; i < numCourses; ++i) {
      if(!degree[i]) {
        answer += 1;
        q.push(i);
      }
    }
    while(q.size()) {
      int cur = q.front();
      q.pop();
      for(auto nxt : edges[cur]) {
        degree[nxt] -= 1;
        if(!degree[nxt]) {
          answer += 1;
          q.push(nxt);
        }
      }
    }
    return answer == numCourses;
  }
};

// Accepted
// 52/52 cases passed (25 ms)
// Your runtime beats 62.83 % of cpp submissions
// Your memory usage beats 83.94 % of cpp submissions (13.2 MB)
Algorithm