Parallel Courses

class Solution {
public:
    int minimumSemesters(int n, vector<vector<int>>& relations) {
        vector<vector<int>> adj(n + 1);
        vector<int> indeg(n + 1, 0);
        for (auto& r : relations) {
            adj[r[0]].push_back(r[1]);
            ++indeg[r[1]];
        }
        queue<int> q;
        for (int i = 1; i <= n; ++i) if (indeg[i] == 0) q.push(i);
        int sem = 0, taken = 0;
        while (!q.empty()) {
            int sz = q.size();
            ++sem;
            taken += sz;
            for (int i = 0; i < sz; ++i) {
                int u = q.front(); q.pop();
                for (int v : adj[u]) if (--indeg[v] == 0) q.push(v);
            }
        }
        return taken == n ? sem : -1;
    }
};

func minimumSemesters(n int, relations [][]int) int {
    adj := make([][]int, n+1)
    indeg := make([]int, n+1)
    for _, r := range relations {
        adj[r[0]] = append(adj[r[0]], r[1])
        indeg[r[1]]++
    }
    q := []int{}
    for i := 1; i <= n; i++ {
        if indeg[i] == 0 {
            q = append(q, i)
        }
    }
    sem, taken := 0, 0
    for len(q) > 0 {
        sz := len(q)
        sem++
        taken += sz
        for i := 0; i < sz; i++ {
            u := q[0]
            q = q[1:]
            for _, v := range adj[u] {
                indeg[v]--
                if indeg[v] == 0 {
                    q = append(q, v)
                }
            }
        }
    }
    if taken == n {
        return sem
    }
    return -1
}

from collections import deque

class Solution:
    def minimumSemesters(self, n: int, relations: List[List[int]]) -> int:
        adj = [[] for _ in range(n + 1)]
        indeg = [0] * (n + 1)
        for a, b in relations:
            adj[a].append(b)
            indeg[b] += 1
        q = deque(i for i in range(1, n + 1) if indeg[i] == 0)
        sem = 0
        taken = 0
        while q:
            sz = len(q)
            sem += 1
            taken += sz
            for _ in range(sz):
                u = q.popleft()
                for v in adj[u]:
                    indeg[v] -= 1
                    if indeg[v] == 0:
                        q.append(v)
        return sem if taken == n else -1

function minimumSemesters(n, relations) {
    const adj = Array.from({ length: n + 1 }, () => []);
    const indeg = new Array(n + 1).fill(0);
    for (const [a, b] of relations) {
        adj[a].push(b);
        indeg[b]++;
    }
    let q = [];
    for (let i = 1; i <= n; i++) if (indeg[i] === 0) q.push(i);
    let sem = 0, taken = 0;
    while (q.length > 0) {
        sem++;
        taken += q.length;
        const next = [];
        for (const u of q) {
            for (const v of adj[u]) {
                if (--indeg[v] === 0) next.push(v);
            }
        }
        q = next;
    }
    return taken === n ? sem : -1;
}

class Solution {
    public int minimumSemesters(int n, int[][] relations) {
        List<List<Integer>> adj = new ArrayList<>();
        for (int i = 0; i <= n; i++) adj.add(new ArrayList<>());
        int[] indeg = new int[n + 1];
        for (int[] r : relations) {
            adj.get(r[0]).add(r[1]);
            indeg[r[1]]++;
        }
        Deque<Integer> q = new ArrayDeque<>();
        for (int i = 1; i <= n; i++) if (indeg[i] == 0) q.offer(i);
        int sem = 0, taken = 0;
        while (!q.isEmpty()) {
            int sz = q.size();
            sem++;
            taken += sz;
            for (int i = 0; i < sz; i++) {
                int u = q.poll();
                for (int v : adj.get(u)) {
                    if (--indeg[v] == 0) q.offer(v);
                }
            }
        }
        return taken == n ? sem : -1;
    }
}

function minimumSemesters(n: number, relations: number[][]): number {
    const adj: number[][] = Array.from({ length: n + 1 }, () => []);
    const indeg: number[] = new Array(n + 1).fill(0);
    for (const [a, b] of relations) {
        adj[a].push(b);
        indeg[b]++;
    }
    let q: number[] = [];
    for (let i = 1; i <= n; i++) if (indeg[i] === 0) q.push(i);
    let sem = 0, taken = 0;
    while (q.length > 0) {
        sem++;
        taken += q.length;
        const next: number[] = [];
        for (const u of q) {
            for (const v of adj[u]) {
                if (--indeg[v] === 0) next.push(v);
            }
        }
        q = next;
    }
    return taken === n ? sem : -1;
}