leetcode题解（五十九）：207. Course Schedule

最新推荐文章于 2021-09-04 09:59:00 发布

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课程安排，输入是课程总数，上课的方式，输出是否可行
Example 1:

Input: 2, [[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: 2, [[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.

public boolean canFinish(int numCourses, int[][] prerequisites) {
    int[][] matrix = new int[numCourses][numCourses]; // i -> j
    int[] indegree = new int[numCourses];
    
    for (int i=0; i<prerequisites.length; i++) {
        int ready = prerequisites[i][0];
        int pre = prerequisites[i][1];
        if (matrix[pre][ready] == 0)
            indegree[ready]++; //duplicate case
        matrix[pre][ready] = 1;
    }
    
    int count = 0;
    Queue<Integer> queue = new LinkedList();
    for (int i=0; i<indegree.length; i++) {
        if (indegree[i] == 0) queue.offer(i);
    }
    while (!queue.isEmpty()) {
        int course = queue.poll();
        count++;
        for (int i=0; i<numCourses; i++) {
            if (matrix[course][i] != 0) {
                if (--indegree[i] == 0)
                    queue.offer(i);
            }
        }
    }
    return count == numCourses;
}