feat: add solutions to lc problem: No.1136

No.1136.Parallel Courses

Author: yanglbme

solution/1100-1199/1136.Parallel Courses/README.md

@@ -57,6 +57,12 @@
 
 **方法一：拓扑排序**
 
+我们可以先将课程之间的先修关系建立图 $g$，并统计每个课程的入度 $indeg$。
+
+然后我们将入度为 $0$ 的课程入队，然后开始进行拓扑排序。每次从队列中取出一个课程，将其出队，并将其出度的课程的入度减 $1$，如果减 $1$ 后入度为 $0$，则将该课程入队。当队列为空时，如果还有课程没有修完，则说明无法修完所有课程，返回 $-1$。否则返回修完所有课程所需的学期数。
+
+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关系数。
+
 <!-- tabs:start -->
 
 ### **Python3**
@@ -68,11 +74,12 @@ class Solution:
     def minimumSemesters(self, n: int, relations: List[List[int]]) -> int:
         g = defaultdict(list)
         indeg = [0] * n
-        for a, b in relations:
-            g[a - 1].append(b - 1)
-            indeg[b - 1] += 1
+        for prev, nxt in relations:
+            prev, nxt = prev - 1, nxt - 1
+            g[prev].append(nxt)
+            indeg[nxt] += 1
+        q = deque(i for i, v in enumerate(indeg) if v == 0)
         ans = 0
-        q = deque([i for i, v in enumerate(indeg) if v == 0])
         while q:
             ans += 1
             for _ in range(len(q)):
@@ -95,10 +102,10 @@ class Solution {
         List<Integer>[] g = new List[n];
         Arrays.setAll(g, k -> new ArrayList<>());
         int[] indeg = new int[n];
-        for (int[] r : relations) {
-            int a = r[0] - 1, b = r[1] - 1;
-            g[a].add(b);
-            ++indeg[b];
+        for (var r : relations) {
+            int prev = r[0] - 1, nxt = r[1] - 1;
+            g[prev].add(nxt);
+            ++indeg[nxt];
         }
         Deque<Integer> q = new ArrayDeque<>();
         for (int i = 0; i < n; ++i) {
@@ -133,22 +140,28 @@ public:
         vector<vector<int>> g(n);
         vector<int> indeg(n);
         for (auto& r : relations) {
-            int a = r[0] - 1, b = r[1] - 1;
-            g[a].push_back(b);
-            ++indeg[b];
+            int prev = r[0] - 1, nxt = r[1] - 1;
+            g[prev].push_back(nxt);
+            ++indeg[nxt];
         }
         queue<int> q;
-        for (int i = 0; i < n; ++i)
-            if (indeg[i] == 0) q.push(i);
+        for (int i = 0; i < n; ++i) {
+            if (indeg[i] == 0) {
+                q.push(i);
+            }
+        }
         int ans = 0;
         while (!q.empty()) {
             ++ans;
             for (int k = q.size(); k; --k) {
                 int i = q.front();
                 q.pop();
                 --n;
-                for (int j : g[i])
-                    if (--indeg[j] == 0) q.push(j);
+                for (int& j : g[i]) {
+                    if (--indeg[j] == 0) {
+                        q.push(j);
+                    }
+                }
             }
         }
         return n == 0 ? ans : -1;
@@ -159,21 +172,20 @@ public:
 ### **Go**
 
 ```go
-func minimumSemesters(n int, relations [][]int) int {
+func minimumSemesters(n int, relations [][]int) (ans int) {
 	g := make([][]int, n)
 	indeg := make([]int, n)
 	for _, r := range relations {
-		a, b := r[0]-1, r[1]-1
-		g[a] = append(g[a], b)
-		indeg[b]++
+		prev, nxt := r[0]-1, r[1]-1
+		g[prev] = append(g[prev], nxt)
+		indeg[nxt]++
 	}
 	q := []int{}
 	for i, v := range indeg {
 		if v == 0 {
 			q = append(q, i)
 		}
 	}
-	ans := 0
 	for len(q) > 0 {
 		ans++
 		for k := len(q); k > 0; k-- {
@@ -189,12 +201,45 @@ func minimumSemesters(n int, relations [][]int) int {
 		}
 	}
 	if n == 0 {
-		return ans
+		return
 	}
 	return -1
 }
 ```
 
+### **TypeScript**
+
+```ts
+function minimumSemesters(n: number, relations: number[][]): number {
+    const g = Array.from({ length: n }, () => []);
+    const indeg = new Array(n).fill(0);
+    for (const [prev, nxt] of relations) {
+        g[prev - 1].push(nxt - 1);
+        indeg[nxt - 1]++;
+    }
+    const q: number[] = [];
+    for (let i = 0; i < n; ++i) {
+        if (indeg[i] === 0) {
+            q.push(i);
+        }
+    }
+    let ans = 0;
+    while (q.length) {
+        ++ans;
+        for (let k = q.length; k; --k) {
+            const i = q.shift()!;
+            --n;
+            for (const j of g[i]) {
+                if (--indeg[j] === 0) {
+                    q.push(j);
+                }
+            }
+        }
+    }
+    return n === 0 ? ans : -1;
+}
+```
+
 ### **...**
 
 ```

solution/1100-1199/1136.Parallel Courses/README_EN.md

@@ -52,11 +52,12 @@ class Solution:
     def minimumSemesters(self, n: int, relations: List[List[int]]) -> int:
         g = defaultdict(list)
         indeg = [0] * n
-        for a, b in relations:
-            g[a - 1].append(b - 1)
-            indeg[b - 1] += 1
+        for prev, nxt in relations:
+            prev, nxt = prev - 1, nxt - 1
+            g[prev].append(nxt)
+            indeg[nxt] += 1
+        q = deque(i for i, v in enumerate(indeg) if v == 0)
         ans = 0
-        q = deque([i for i, v in enumerate(indeg) if v == 0])
         while q:
             ans += 1
             for _ in range(len(q)):
@@ -77,10 +78,10 @@ class Solution {
         List<Integer>[] g = new List[n];
         Arrays.setAll(g, k -> new ArrayList<>());
         int[] indeg = new int[n];
-        for (int[] r : relations) {
-            int a = r[0] - 1, b = r[1] - 1;
-            g[a].add(b);
-            ++indeg[b];
+        for (var r : relations) {
+            int prev = r[0] - 1, nxt = r[1] - 1;
+            g[prev].add(nxt);
+            ++indeg[nxt];
         }
         Deque<Integer> q = new ArrayDeque<>();
         for (int i = 0; i < n; ++i) {
@@ -115,22 +116,28 @@ public:
         vector<vector<int>> g(n);
         vector<int> indeg(n);
         for (auto& r : relations) {
-            int a = r[0] - 1, b = r[1] - 1;
-            g[a].push_back(b);
-            ++indeg[b];
+            int prev = r[0] - 1, nxt = r[1] - 1;
+            g[prev].push_back(nxt);
+            ++indeg[nxt];
         }
         queue<int> q;
-        for (int i = 0; i < n; ++i)
-            if (indeg[i] == 0) q.push(i);
+        for (int i = 0; i < n; ++i) {
+            if (indeg[i] == 0) {
+                q.push(i);
+            }
+        }
         int ans = 0;
         while (!q.empty()) {
             ++ans;
             for (int k = q.size(); k; --k) {
                 int i = q.front();
                 q.pop();
                 --n;
-                for (int j : g[i])
-                    if (--indeg[j] == 0) q.push(j);
+                for (int& j : g[i]) {
+                    if (--indeg[j] == 0) {
+                        q.push(j);
+                    }
+                }
             }
         }
         return n == 0 ? ans : -1;
@@ -141,21 +148,20 @@ public:
 ### **Go**
 
 ```go
-func minimumSemesters(n int, relations [][]int) int {
+func minimumSemesters(n int, relations [][]int) (ans int) {
 	g := make([][]int, n)
 	indeg := make([]int, n)
 	for _, r := range relations {
-		a, b := r[0]-1, r[1]-1
-		g[a] = append(g[a], b)
-		indeg[b]++
+		prev, nxt := r[0]-1, r[1]-1
+		g[prev] = append(g[prev], nxt)
+		indeg[nxt]++
 	}
 	q := []int{}
 	for i, v := range indeg {
 		if v == 0 {
 			q = append(q, i)
 		}
 	}
-	ans := 0
 	for len(q) > 0 {
 		ans++
 		for k := len(q); k > 0; k-- {
@@ -171,12 +177,45 @@ func minimumSemesters(n int, relations [][]int) int {
 		}
 	}
 	if n == 0 {
-		return ans
+		return
 	}
 	return -1
 }
 ```
 
+### **TypeScript**
+
+```ts
+function minimumSemesters(n: number, relations: number[][]): number {
+    const g = Array.from({ length: n }, () => []);
+    const indeg = new Array(n).fill(0);
+    for (const [prev, nxt] of relations) {
+        g[prev - 1].push(nxt - 1);
+        indeg[nxt - 1]++;
+    }
+    const q: number[] = [];
+    for (let i = 0; i < n; ++i) {
+        if (indeg[i] === 0) {
+            q.push(i);
+        }
+    }
+    let ans = 0;
+    while (q.length) {
+        ++ans;
+        for (let k = q.length; k; --k) {
+            const i = q.shift()!;
+            --n;
+            for (const j of g[i]) {
+                if (--indeg[j] === 0) {
+                    q.push(j);
+                }
+            }
+        }
+    }
+    return n === 0 ? ans : -1;
+}
+```
+
 ### **...**
 
 ```

solution/1100-1199/1136.Parallel Courses/Solution.cpp

@@ -4,22 +4,28 @@ class Solution {
         vector<vector<int>> g(n);
         vector<int> indeg(n);
         for (auto& r : relations) {
-            int a = r[0] - 1, b = r[1] - 1;
-            g[a].push_back(b);
-            ++indeg[b];
+            int prev = r[0] - 1, nxt = r[1] - 1;
+            g[prev].push_back(nxt);
+            ++indeg[nxt];
         }
         queue<int> q;
-        for (int i = 0; i < n; ++i)
-            if (indeg[i] == 0) q.push(i);
+        for (int i = 0; i < n; ++i) {
+            if (indeg[i] == 0) {
+                q.push(i);
+            }
+        }
         int ans = 0;
         while (!q.empty()) {
             ++ans;
             for (int k = q.size(); k; --k) {
                 int i = q.front();
                 q.pop();
                 --n;
-                for (int j : g[i])
-                    if (--indeg[j] == 0) q.push(j);
+                for (int& j : g[i]) {
+                    if (--indeg[j] == 0) {
+                        q.push(j);
+                    }
+                }
             }
         }
         return n == 0 ? ans : -1;

solution/1100-1199/1136.Parallel Courses/Solution.go

@@ -1,18 +1,17 @@
-func minimumSemesters(n int, relations [][]int) int {
+func minimumSemesters(n int, relations [][]int) (ans int) {
 	g := make([][]int, n)
 	indeg := make([]int, n)
 	for _, r := range relations {
-		a, b := r[0]-1, r[1]-1
-		g[a] = append(g[a], b)
-		indeg[b]++
+		prev, nxt := r[0]-1, r[1]-1
+		g[prev] = append(g[prev], nxt)
+		indeg[nxt]++
 	}
 	q := []int{}
 	for i, v := range indeg {
 		if v == 0 {
 			q = append(q, i)
 		}
 	}
-	ans := 0
 	for len(q) > 0 {
 		ans++
 		for k := len(q); k > 0; k-- {
@@ -28,7 +27,7 @@ func minimumSemesters(n int, relations [][]int) int {
 		}
 	}
 	if n == 0 {
-		return ans
+		return
 	}
 	return -1
 }

solution/1100-1199/1136.Parallel Courses/Solution.java

@@ -3,10 +3,10 @@ public int minimumSemesters(int n, int[][] relations) {
         List<Integer>[] g = new List[n];
         Arrays.setAll(g, k -> new ArrayList<>());
         int[] indeg = new int[n];
-        for (int[] r : relations) {
-            int a = r[0] - 1, b = r[1] - 1;
-            g[a].add(b);
-            ++indeg[b];
+        for (var r : relations) {
+            int prev = r[0] - 1, nxt = r[1] - 1;
+            g[prev].add(nxt);
+            ++indeg[nxt];
         }
         Deque<Integer> q = new ArrayDeque<>();
         for (int i = 0; i < n; ++i) {

solution/1100-1199/1136.Parallel Courses/Solution.py

@@ -2,11 +2,12 @@ class Solution:
     def minimumSemesters(self, n: int, relations: List[List[int]]) -> int:
         g = defaultdict(list)
         indeg = [0] * n
-        for a, b in relations:
-            g[a - 1].append(b - 1)
-            indeg[b - 1] += 1
+        for prev, nxt in relations:
+            prev, nxt = prev - 1, nxt - 1
+            g[prev].append(nxt)
+            indeg[nxt] += 1
+        q = deque(i for i, v in enumerate(indeg) if v == 0)
         ans = 0
-        q = deque([i for i, v in enumerate(indeg) if v == 0])
         while q:
             ans += 1
             for _ in range(len(q)):