feat: add solutions to lc problem: No.0207 (#3915)

No.0207.Course Schedule

Author: yanglbme

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

@@ -80,21 +80,19 @@ tags:
 ```python
 class Solution:
     def canFinish(self, numCourses: int, prerequisites: List[List[int]]) -> bool:
-        g = defaultdict(list)
+        g = [[] for _ in range(numCourses)]
         indeg = [0] * numCourses
         for a, b in prerequisites:
             g[b].append(a)
             indeg[a] += 1
-        cnt = 0
-        q = deque(i for i, x in enumerate(indeg) if x == 0)
-        while q:
-            i = q.popleft()
-            cnt += 1
+        q = [i for i, x in enumerate(indeg) if x == 0]
+        for i in q:
+            numCourses -= 1
             for j in g[i]:
                 indeg[j] -= 1
                 if indeg[j] == 0:
                     q.append(j)
-        return cnt == numCourses
+        return numCourses == 0
 ```
 
 #### Java
@@ -116,17 +114,16 @@ class Solution {
                 q.offer(i);
             }
         }
-        int cnt = 0;
         while (!q.isEmpty()) {
             int i = q.poll();
-            ++cnt;
+            --numCourses;
             for (int j : g[i]) {
                 if (--indeg[j] == 0) {
                     q.offer(j);
                 }
             }
         }
-        return cnt == numCourses;
+        return numCourses == 0;
     }
 }
 ```
@@ -150,18 +147,17 @@ public:
                 q.push(i);
             }
         }
-        int cnt = 0;
         while (!q.empty()) {
             int i = q.front();
             q.pop();
-            ++cnt;
+            --numCourses;
             for (int j : g[i]) {
                 if (--indeg[j] == 0) {
                     q.push(j);
                 }
             }
         }
-        return cnt == numCourses;
+        return numCourses == 0;
     }
 };
 ```
@@ -183,49 +179,46 @@ func canFinish(numCourses int, prerequisites [][]int) bool {
 			q = append(q, i)
 		}
 	}
-	cnt := 0
 	for len(q) > 0 {
 		i := q[0]
 		q = q[1:]
-		cnt++
+		numCourses--
 		for _, j := range g[i] {
 			indeg[j]--
 			if indeg[j] == 0 {
 				q = append(q, j)
 			}
 		}
 	}
-	return cnt == numCourses
+	return numCourses == 0
 }
 ```
 
 #### TypeScript
 
 ```ts
 function canFinish(numCourses: number, prerequisites: number[][]): boolean {
-    const g: number[][] = new Array(numCourses).fill(0).map(() => []);
-    const indeg: number[] = new Array(numCourses).fill(0);
+    const g: number[][] = Array.from({ length: numCourses }, () => []);
+    const indeg: number[] = Array(numCourses).fill(0);
     for (const [a, b] of prerequisites) {
         g[b].push(a);
         indeg[a]++;
     }
     const q: number[] = [];
     for (let i = 0; i < numCourses; ++i) {
-        if (indeg[i] == 0) {
+        if (indeg[i] === 0) {
             q.push(i);
         }
     }
-    let cnt = 0;
-    while (q.length) {
-        const i = q.shift()!;
-        cnt++;
+    for (const i of q) {
+        --numCourses;
         for (const j of g[i]) {
-            if (--indeg[j] == 0) {
+            if (--indeg[j] === 0) {
                 q.push(j);
             }
         }
     }
-    return cnt == numCourses;
+    return numCourses === 0;
 }
 ```
 
@@ -235,48 +228,36 @@ function canFinish(numCourses: number, prerequisites: number[][]): boolean {
 use std::collections::VecDeque;
 
 impl Solution {
-    #[allow(dead_code)]
-    pub fn can_finish(num_course: i32, prerequisites: Vec<Vec<i32>>) -> bool {
-        let num_course = num_course as usize;
-        // The graph representation
-        let mut graph: Vec<Vec<i32>> = vec![vec![]; num_course];
-        // Record the in degree for each node
-        let mut in_degree_vec: Vec<i32> = vec![0; num_course];
-        let mut q: VecDeque<usize> = VecDeque::new();
-        let mut count = 0;
-
-        // Initialize the graph & in degree vector
-        for p in &prerequisites {
-            let (from, to) = (p[0], p[1]);
-            graph[from as usize].push(to);
-            in_degree_vec[to as usize] += 1;
+    pub fn can_finish(mut num_courses: i32, prerequisites: Vec<Vec<i32>>) -> bool {
+        let mut g: Vec<Vec<i32>> = vec![vec![]; num_courses as usize];
+        let mut indeg: Vec<i32> = vec![0; num_courses as usize];
+
+        for p in prerequisites {
+            let a = p[0] as usize;
+            let b = p[1] as usize;
+            g[b].push(a as i32);
+            indeg[a] += 1;
         }
 
-        // Enqueue the first batch of nodes with in degree 0
-        for i in 0..num_course {
-            if in_degree_vec[i] == 0 {
-                q.push_back(i);
+        let mut q: VecDeque<usize> = VecDeque::new();
+        for i in 0..num_courses {
+            if indeg[i as usize] == 0 {
+                q.push_back(i as usize);
             }
         }
 
-        // Begin the traverse & update through the graph
-        while !q.is_empty() {
-            // Get the current node index
-            let index = q.front().unwrap().clone();
-            // This course can be finished
-            count += 1;
-            q.pop_front();
-            for i in &graph[index] {
-                // Update the in degree for the current node
-                in_degree_vec[*i as usize] -= 1;
-                // See if can be enqueued
-                if in_degree_vec[*i as usize] == 0 {
-                    q.push_back(*i as usize);
+        while let Some(i) = q.pop_front() {
+            num_courses -= 1;
+            for &j in &g[i] {
+                let j = j as usize;
+                indeg[j] -= 1;
+                if indeg[j] == 0 {
+                    q.push_back(j);
                 }
             }
         }
 
-        count == num_course
+        num_courses == 0
     }
 }
 ```