問題
Courses are numbered 0..n−1. Each pair [course, prerequisite] means the prerequisite must be taken before the course. Return an order to take all courses; when several courses are available, take the lowest-numbered one first so the answer is unique.
Implement course_order(n, prerequisites).
Input
n: The number of courses. prerequisites: Pairs [course, prerequisite].
Output
Return the course order, or an empty list if a cycle makes it impossible.
制約
1 ≤ n ≤ 100,000; 0 ≤ pairs ≤ 200,000
例
例 1
入力：
n = 4
prerequisites = [
[1, 0],
[2, 0],
[3, 1],
[3, 2]
]
期待される出力：
expected = [0, 1, 2, 3]入力：
long long n = 4;
std::vector<std::vector<long long>> prerequisites = {
{1, 0},
{2, 0},
{3, 1},
{3, 2}
};
期待される出力：
std::vector<long long> expected = {0, 1, 2, 3};入力：
long n = 4;
long[][] prerequisites = new long[][] {
new long[] {1, 0},
new long[] {2, 0},
new long[] {3, 1},
new long[] {3, 2}
};
期待される出力：
long[] expected = new long[] {0, 1, 2, 3};解説
0 first, then 1 and 2 (lowest first), then 3: [0, 1, 2, 3].
例 2
入力：
n = 2
prerequisites = [
[0, 1],
[1, 0]
]
期待される出力：
expected = []入力：
long long n = 2;
std::vector<std::vector<long long>> prerequisites = {
{0, 1},
{1, 0}
};
期待される出力：
std::vector<long long> expected = {};入力：
long n = 2;
long[][] prerequisites = new long[][] {
new long[] {0, 1},
new long[] {1, 0}
};
期待される出力：
long[] expected = new long[] {};解説
Each course requires the other, so no order exists: [].
参考資料
この課題はCodeUtility用に調整されています。上記の説明と制約に従ってください。