@@ -48,13 +48,136 @@ In the second semester, you can take course 3.
4848### ** Python3**
4949
5050``` python
51- 51+ class Solution :
52+ def minimumSemesters (self n : int , relations : List[List[int ]]) -> int :
53+ g = defaultdict(list )
54+ indeg = [0 ] * n
55+ for a, b in relations:
56+ g[a - 1 ].append(b - 1 )
57+ indeg[b - 1 ] += 1
58+ ans = 0
59+ q = deque([i for i, v in enumerate (indeg) if v == 0 ])
60+ while q:
61+ ans += 1
62+ for _ in range (len (q)):
63+ i = q.popleft()
64+ n -= 1
65+ for j in g[i]:
66+ indeg[j] -= 1
67+ if indeg[j] == 0 :
68+ q.append(j)
69+ return - 1 if n else ans
5270```
5371
5472### ** Java**
5573
5674``` java
75+ class Solution {
76+ public int minimumSemesters (int n , int [][] relations ) {
77+ List<Integer > [] g = new List [n];
78+ for (int i = 0 ; i < n; ++ i) {
79+ g[i] = new ArrayList<> ();
80+ }
81+ int [] indeg = new int [n];
82+ for (int [] r : relations) {
83+ int a = r[0 ] - 1 , b = r[1 ] - 1 ;
84+ g[a]. add(b);
85+ ++ indeg[b];
86+ }
87+ Deque<Integer > q = new ArrayDeque<> ();
88+ for (int i = 0 ; i < n; ++ i) {
89+ if (indeg[i] == 0 ) {
90+ q. offer(i);
91+ }
92+ }
93+ int ans = 0 ;
94+ while (! q. isEmpty()) {
95+ ++ ans;
96+ for (int k = q. size(); k > 0 ; -- k) {
97+ int i = q. poll();
98+ -- n;
99+ for (int j : g[i]) {
100+ if (-- indeg[j] == 0 ) {
101+ q. offer(j);
102+ }
103+ }
104+ }
105+ }
106+ return n == 0 ? ans : - 1 ;
107+ }
108+ }
109+ ```
110+ 111+ ### ** C++**
112+ 113+ ``` cpp
114+ class Solution {
115+ public:
116+ int minimumSemesters(int n, vector<vector<int >>& relations) {
117+ vector<vector<int >> g(n);
118+ vector<int > indeg(n);
119+ for (auto& r : relations)
120+ {
121+ int a = r[ 0] - 1, b = r[ 1] - 1;
122+ g[ a] .push_back(b);
123+ ++indeg[ b] ;
124+ }
125+ queue<int > q;
126+ for (int i = 0; i < n; ++i) if (indeg[ i] == 0) q.push(i);
127+ int ans = 0;
128+ while (!q.empty())
129+ {
130+ ++ans;
131+ for (int k = q.size(); k; --k)
132+ {
133+ int i = q.front();
134+ q.pop();
135+ --n;
136+ for (int j : g[ i] ) if (--indeg[ j] == 0) q.push(j);
137+ }
138+ }
139+ return n == 0 ? ans : -1;
140+ }
141+ };
142+ ```
57143
144+ ### **Go**
145+
146+ ```go
147+ func minimumSemesters(n int, relations [][]int) int {
148+ g := make([][]int, n)
149+ indeg := make([]int, n)
150+ for _, r := range relations {
151+ a, b := r[0]-1, r[1]-1
152+ g[a] = append(g[a], b)
153+ indeg[b]++
154+ }
155+ q := []int{}
156+ for i, v := range indeg {
157+ if v == 0 {
158+ q = append(q, i)
159+ }
160+ }
161+ ans := 0
162+ for len(q) > 0 {
163+ ans++
164+ for k := len(q); k > 0; k-- {
165+ i := q[0]
166+ q = q[1:]
167+ n--
168+ for _, j := range g[i] {
169+ indeg[j]--
170+ if indeg[j] == 0 {
171+ q = append(q, j)
172+ }
173+ }
174+ }
175+ }
176+ if n == 0 {
177+ return ans
178+ }
179+ return -1
180+ }
58181```
59182
60183### ** ...**
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