@@ -80,21 +80,19 @@ tags:
8080``` python
8181class Solution :
8282 def canFinish (self numCourses : int , prerequisites : List[List[int ]]) -> bool :
83- g = defaultdict( list )
83+ g = [[] for _ in range (numCourses)]
8484 indeg = [0 ] * numCourses
8585 for a, b in prerequisites:
8686 g[b].append(a)
8787 indeg[a] += 1
88- cnt = 0
89- q = deque(i for i, x in enumerate (indeg) if x == 0 )
90- while q:
91- i = q.popleft()
92- cnt += 1
88+ q = [i for i, x in enumerate (indeg) if x == 0 ]
89+ for i in q:
90+ numCourses -= 1
9391 for j in g[i]:
9492 indeg[j] -= 1
9593 if indeg[j] == 0 :
9694 q.append(j)
97- return cnt == numCourses
95+ return numCourses == 0
9896```
9997
10098#### Java
@@ -116,17 +114,16 @@ class Solution {
116114 q. offer(i);
117115 }
118116 }
119- int cnt = 0 ;
120117 while (! q. isEmpty()) {
121118 int i = q. poll();
122- ++ cnt ;
119+ -- numCourses ;
123120 for (int j : g[i]) {
124121 if (-- indeg[j] == 0 ) {
125122 q. offer(j);
126123 }
127124 }
128125 }
129- return cnt == numCourses ;
126+ return numCourses == 0 ;
130127 }
131128}
132129```
@@ -150,18 +147,17 @@ public:
150147 q.push(i);
151148 }
152149 }
153- int cnt = 0;
154150 while (!q.empty()) {
155151 int i = q.front();
156152 q.pop();
157- ++cnt ;
153+ --numCourses ;
158154 for (int j : g[ i] ) {
159155 if (--indeg[ j] == 0) {
160156 q.push(j);
161157 }
162158 }
163159 }
164- return cnt == numCourses ;
160+ return numCourses == 0 ;
165161 }
166162};
167163```
@@ -183,49 +179,46 @@ func canFinish(numCourses int, prerequisites [][]int) bool {
183179 q = append(q, i)
184180 }
185181 }
186- cnt := 0
187182 for len(q) > 0 {
188183 i := q[0]
189184 q = q[1:]
190- cnt++
185+ numCourses--
191186 for _, j := range g[i] {
192187 indeg[j]--
193188 if indeg[j] == 0 {
194189 q = append(q, j)
195190 }
196191 }
197192 }
198- return cnt == numCourses
193+ return numCourses == 0
199194}
200195```
201196
202197#### TypeScript
203198
204199``` ts
205200function canFinish(numCourses : number , prerequisites : number [][]): boolean {
206- const : number [][] = new Array ( numCourses ). fill ( 0 ). map ( () => []);
207- const : number [] = new Array (numCourses ).fill (0 );
201+ const : number [][] = Array . from ({ length: numCourses }, () => []);
202+ const : number [] = Array (numCourses ).fill (0 );
208203 for (const of prerequisites ) {
209204 g [b ].push (a );
210205 indeg [a ]++ ;
211206 }
212207 const : number [] = [];
213208 for (let i = 0 ; i < numCourses ; ++ i ) {
214- if (indeg [i ] == 0 ) {
209+ if (indeg [i ] === 0 ) {
215210 q .push (i );
216211 }
217212 }
218- let cnt = 0 ;
219- while (q .length ) {
220- const = q .shift ()! ;
221- cnt ++ ;
213+ for (const of q ) {
214+ -- numCourses ;
222215 for (const of g [i ]) {
223- if (-- indeg [j ] == 0 ) {
216+ if (-- indeg [j ] === 0 ) {
224217 q .push (j );
225218 }
226219 }
227220 }
228- return cnt == numCourses ;
221+ return numCourses === 0 ;
229222}
230223```
231224
@@ -235,48 +228,36 @@ function canFinish(numCourses: number, prerequisites: number[][]): boolean {
235228use std :: collections :: VecDeque ;
236229
237230impl Solution {
238- #[allow(dead_code)]
239- pub fn can_finish (num_course : i32 , prerequisites : Vec <Vec <i32 >>) -> bool {
240- let num_course = num_course as usize ;
241- // The graph representation
242- let mut graph : Vec <Vec <i32 >> = vec! [vec! []; num_course ];
243- // Record the in degree for each node
244- let mut in_degree_vec : Vec <i32 > = vec! [0 ; num_course ];
245- let mut q : VecDeque <usize > = VecDeque :: new ();
246- let mut count = 0 ;
247- 248- // Initialize the graph & in degree vector
249- for p in & prerequisites {
250- let (from , to ) = (p [0 ], p [1 ]);
251- graph [from as usize ]. push (to );
252- in_degree_vec [to as usize ] += 1 ;
231+ pub fn can_finish (mut num_courses : i32 , prerequisites : Vec <Vec <i32 >>) -> bool {
232+ let mut g : Vec <Vec <i32 >> = vec! [vec! []; num_courses as usize ];
233+ let mut indeg : Vec <i32 > = vec! [0 ; num_courses as usize ];
234+ 235+ for p in prerequisites {
236+ let a = p [0 ] as usize ;
237+ let b = p [1 ] as usize ;
238+ g [b ]. push (a as i32 );
239+ indeg [a ] += 1 ;
253240 }
254241
255- // Enqueue the first batch of nodes with in degree 0
256- for i in 0 .. num_course {
257- if in_degree_vec [ i ] == 0 {
258- q . push_back (i );
242+ let mut q : VecDeque < usize > = VecDeque :: new ();
243+ for i in 0 .. num_courses {
244+ if indeg [ i as usize ] == 0 {
245+ q . push_back (i as usize );
259246 }
260247 }
261248
262- // Begin the traverse & update through the graph
263- while ! q . is_empty () {
264- // Get the current node index
265- let index = q . front (). unwrap (). clone ();
266- // This course can be finished
267- count += 1 ;
268- q . pop_front ();
269- for i in & graph [index ] {
270- // Update the in degree for the current node
271- in_degree_vec [* i as usize ] -= 1 ;
272- // See if can be enqueued
273- if in_degree_vec [* i as usize ] == 0 {
274- q . push_back (* i as usize );
249+ while let Some (i ) = q . pop_front () {
250+ num_courses -= 1 ;
251+ for & j in & g [i ] {
252+ let j = j as usize ;
253+ indeg [j ] -= 1 ;
254+ if indeg [j ] == 0 {
255+ q . push_back (j );
275256 }
276257 }
277258 }
278259
279- count == num_course
260+ num_courses == 0
280261 }
281262}
282263```
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