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feat: add solutions to lc problem: No.0207
No.0207.Course Schedule
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-127
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‎solution/0200-0299/0207.Course Schedule/README.md

+61-50
Original file line numberDiff line numberDiff line change
@@ -50,7 +50,13 @@
5050

5151
**方法一：拓扑排序**
5252

53-
BFS 实现。
53+
对于本题，我们可以将课程看作图中的节点，先修课程看作图中的边，那么我们可以将本题转化为判断有向图中是否存在环。
54+
55+
具体地，我们可以使用拓扑排序的思想，对于每个入度为 $0$ 的节点，我们将其出度的节点的入度减 $1$，直到所有节点都被遍历到。
56+
57+
如果所有节点都被遍历到，说明图中不存在环，那么我们就可以完成所有课程的学习；否则，我们就无法完成所有课程的学习。
58+
59+
时间复杂度 $O(n + m)$，空间复杂度 $O(n + m)$。其中 $n$ 和 $m$ 分别为课程数和先修课程数。
5460

5561
<!-- tabs:start -->
5662

@@ -67,7 +73,7 @@ class Solution:
6773
g[b].append(a)
6874
indeg[a] += 1
6975
cnt = 0
70-
q = deque([i for i, v in enumerate(indeg) if v == 0])
76+
q = deque(i for i, x in enumerate(indeg) if x == 0)
7177
while q:
7278
i = q.popleft()
7379
cnt += 1
@@ -114,36 +120,6 @@ class Solution {
114120
}
115121
```
116122

117-
### **TypeScrpt**
118-
119-
```ts
120-
function canFinish(numCourses: number, prerequisites: number[][]): boolean {
121-
let g = Array.from({ length: numCourses }, () => []);
122-
let indeg = new Array(numCourses).fill(0);
123-
for (let [a, b] of prerequisites) {
124-
g[b].push(a);
125-
++indeg[a];
126-
}
127-
let q = [];
128-
for (let i = 0; i < numCourses; ++i) {
129-
if (!indeg[i]) {
130-
q.push(i);
131-
}
132-
}
133-
let cnt = 0;
134-
while (q.length) {
135-
const i = q.shift();
136-
++cnt;
137-
for (let j of g[i]) {
138-
if (--indeg[j] == 0) {
139-
q.push(j);
140-
}
141-
}
142-
}
143-
return cnt == numCourses;
144-
}
145-
```
146-
147123
### **C++**
148124

149125
```cpp
@@ -158,15 +134,21 @@ public:
158134
++indeg[a];
159135
}
160136
queue<int> q;
161-
for (int i = 0; i < numCourses; ++i)
162-
if (indeg[i] == 0) q.push(i);
137+
for (int i = 0; i < numCourses; ++i) {
138+
if (indeg[i] == 0) {
139+
q.push(i);
140+
}
141+
}
163142
int cnt = 0;
164143
while (!q.empty()) {
165144
int i = q.front();
166145
q.pop();
167146
++cnt;
168-
for (int j : g[i])
169-
if (--indeg[j] == 0) q.push(j);
147+
for (int j : g[i]) {
148+
if (--indeg[j] == 0) {
149+
q.push(j);
150+
}
151+
}
170152
}
171153
return cnt == numCourses;
172154
}
@@ -185,8 +167,8 @@ func canFinish(numCourses int, prerequisites [][]int) bool {
185167
indeg[a]++
186168
}
187169
q := []int{}
188-
for i, v := range indeg {
189-
if v == 0 {
170+
for i, x := range indeg {
171+
if x == 0 {
190172
q = append(q, i)
191173
}
192174
}
@@ -206,36 +188,65 @@ func canFinish(numCourses int, prerequisites [][]int) bool {
206188
}
207189
```
208190

191+
### **TypeScript**
192+
193+
```ts
194+
function canFinish(numCourses: number, prerequisites: number[][]): boolean {
195+
const g: number[][] = new Array(numCourses).fill(0).map(() => []);
196+
const indeg: number[] = new Array(numCourses).fill(0);
197+
for (const [a, b] of prerequisites) {
198+
g[b].push(a);
199+
indeg[a]++;
200+
}
201+
const q: number[] = [];
202+
for (let i = 0; i < numCourses; ++i) {
203+
if (indeg[i] == 0) {
204+
q.push(i);
205+
}
206+
}
207+
let cnt = 0;
208+
while (q.length) {
209+
const i = q.shift()!;
210+
cnt++;
211+
for (const j of g[i]) {
212+
if (--indeg[j] == 0) {
213+
q.push(j);
214+
}
215+
}
216+
}
217+
return cnt == numCourses;
218+
}
219+
```
220+
209221
### **C#**
210222

211223
```cs
212224
public class Solution {
213225
public bool CanFinish(int numCourses, int[][] prerequisites) {
214226
var g = new List<int>[numCourses];
215-
for (int i = 0; i < numCourses; ++i)
216-
{
227+
for (int i = 0; i < numCourses; ++i) {
217228
g[i] = new List<int>();
218229
}
219230
var indeg = new int[numCourses];
220-
foreach (var p in prerequisites)
221-
{
231+
foreach (var p in prerequisites) {
222232
int a = p[0], b = p[1];
223233
g[b].Add(a);
224234
++indeg[a];
225235
}
226236
var q = new Queue<int>();
227-
for (int i = 0; i < numCourses; ++i)
228-
{
229-
if (indeg[i] == 0) q.Enqueue(i);
237+
for (int i = 0; i < numCourses; ++i) {
238+
if (indeg[i] == 0) {
239+
q.Enqueue(i);
240+
}
230241
}
231242
var cnt = 0;
232-
while (q.Count > 0)
233-
{
243+
while (q.Count > 0) {
234244
int i = q.Dequeue();
235245
++cnt;
236-
foreach (int j in g[i])
237-
{
238-
if (--indeg[j] == 0) q.Enqueue(j);
246+
foreach (int j in g[i]) {
247+
if (--indeg[j] == 0) {
248+
q.Enqueue(j);
249+
}
239250
}
240251
}
241252
return cnt == numCourses;

‎solution/0200-0299/0207.Course Schedule/README_EN.md

+54-49
Original file line numberDiff line numberDiff line change
@@ -57,7 +57,7 @@ class Solution:
5757
g[b].append(a)
5858
indeg[a] += 1
5959
cnt = 0
60-
q = deque([i for i, v in enumerate(indeg) if v == 0])
60+
q = deque(i for i, x in enumerate(indeg) if x == 0)
6161
while q:
6262
i = q.popleft()
6363
cnt += 1
@@ -102,36 +102,6 @@ class Solution {
102102
}
103103
```
104104

105-
### **TypeScript**
106-
107-
```ts
108-
function canFinish(numCourses: number, prerequisites: number[][]): boolean {
109-
let g = Array.from({ length: numCourses }, () => []);
110-
let indeg = new Array(numCourses).fill(0);
111-
for (let [a, b] of prerequisites) {
112-
g[b].push(a);
113-
++indeg[a];
114-
}
115-
let q = [];
116-
for (let i = 0; i < numCourses; ++i) {
117-
if (!indeg[i]) {
118-
q.push(i);
119-
}
120-
}
121-
let cnt = 0;
122-
while (q.length) {
123-
const i = q.shift();
124-
++cnt;
125-
for (let j of g[i]) {
126-
if (--indeg[j] == 0) {
127-
q.push(j);
128-
}
129-
}
130-
}
131-
return cnt == numCourses;
132-
}
133-
```
134-
135105
### **C++**
136106

137107
```cpp
@@ -146,15 +116,21 @@ public:
146116
++indeg[a];
147117
}
148118
queue<int> q;
149-
for (int i = 0; i < numCourses; ++i)
150-
if (indeg[i] == 0) q.push(i);
119+
for (int i = 0; i < numCourses; ++i) {
120+
if (indeg[i] == 0) {
121+
q.push(i);
122+
}
123+
}
151124
int cnt = 0;
152125
while (!q.empty()) {
153126
int i = q.front();
154127
q.pop();
155128
++cnt;
156-
for (int j : g[i])
157-
if (--indeg[j] == 0) q.push(j);
129+
for (int j : g[i]) {
130+
if (--indeg[j] == 0) {
131+
q.push(j);
132+
}
133+
}
158134
}
159135
return cnt == numCourses;
160136
}
@@ -173,8 +149,8 @@ func canFinish(numCourses int, prerequisites [][]int) bool {
173149
indeg[a]++
174150
}
175151
q := []int{}
176-
for i, v := range indeg {
177-
if v == 0 {
152+
for i, x := range indeg {
153+
if x == 0 {
178154
q = append(q, i)
179155
}
180156
}
@@ -194,36 +170,65 @@ func canFinish(numCourses int, prerequisites [][]int) bool {
194170
}
195171
```
196172

173+
### **TypeScript**
174+
175+
```ts
176+
function canFinish(numCourses: number, prerequisites: number[][]): boolean {
177+
const g: number[][] = new Array(numCourses).fill(0).map(() => []);
178+
const indeg: number[] = new Array(numCourses).fill(0);
179+
for (const [a, b] of prerequisites) {
180+
g[b].push(a);
181+
indeg[a]++;
182+
}
183+
const q: number[] = [];
184+
for (let i = 0; i < numCourses; ++i) {
185+
if (indeg[i] == 0) {
186+
q.push(i);
187+
}
188+
}
189+
let cnt = 0;
190+
while (q.length) {
191+
const i = q.shift()!;
192+
cnt++;
193+
for (const j of g[i]) {
194+
if (--indeg[j] == 0) {
195+
q.push(j);
196+
}
197+
}
198+
}
199+
return cnt == numCourses;
200+
}
201+
```
202+
197203
### **C#**
198204

199205
```cs
200206
public class Solution {
201207
public bool CanFinish(int numCourses, int[][] prerequisites) {
202208
var g = new List<int>[numCourses];
203-
for (int i = 0; i < numCourses; ++i)
204-
{
209+
for (int i = 0; i < numCourses; ++i) {
205210
g[i] = new List<int>();
206211
}
207212
var indeg = new int[numCourses];
208-
foreach (var p in prerequisites)
209-
{
213+
foreach (var p in prerequisites) {
210214
int a = p[0], b = p[1];
211215
g[b].Add(a);
212216
++indeg[a];
213217
}
214218
var q = new Queue<int>();
215-
for (int i = 0; i < numCourses; ++i)
216-
{
217-
if (indeg[i] == 0) q.Enqueue(i);
219+
for (int i = 0; i < numCourses; ++i) {
220+
if (indeg[i] == 0) {
221+
q.Enqueue(i);
222+
}
218223
}
219224
var cnt = 0;
220-
while (q.Count > 0)
221-
{
225+
while (q.Count > 0) {
222226
int i = q.Dequeue();
223227
++cnt;
224-
foreach (int j in g[i])
225-
{
226-
if (--indeg[j] == 0) q.Enqueue(j);
228+
foreach (int j in g[i]) {
229+
if (--indeg[j] == 0) {
230+
q.Enqueue(j);
231+
}
227232
}
228233
}
229234
return cnt == numCourses;

‎solution/0200-0299/0207.Course Schedule/Solution.cpp

+10-4
Original file line numberDiff line numberDiff line change
@@ -9,15 +9,21 @@ class Solution {
99
++indeg[a];
1010
}
1111
queue<int> q;
12-
for (int i = 0; i < numCourses; ++i)
13-
if (indeg[i] == 0) q.push(i);
12+
for (int i = 0; i < numCourses; ++i) {
13+
if (indeg[i] == 0) {
14+
q.push(i);
15+
}
16+
}
1417
int cnt = 0;
1518
while (!q.empty()) {
1619
int i = q.front();
1720
q.pop();
1821
++cnt;
19-
for (int j : g[i])
20-
if (--indeg[j] == 0) q.push(j);
22+
for (int j : g[i]) {
23+
if (--indeg[j] == 0) {
24+
q.push(j);
25+
}
26+
}
2127
}
2228
return cnt == numCourses;
2329
}

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