规范格式

leetcode/0207.Course-Schedule/207. Course Schedule.go

@@ -0,0 +1,28 @@
+package leetcode
+
+// AOV 网的拓扑排序
+func canFinish(n int, pre [][]int) bool {
+	in := make([]int, n)
+	frees := make([][]int, n)
+	next := make([]int, 0, n)
+	for _, v := range pre {
+		in[v[0]]++
+		frees[v[1]] = append(frees[v[1]], v[0])
+	}
+	for i := 0; i < n; i++ {
+		if in[i] == 0 {
+			next = append(next, i)
+		}
+	}
+	for i := 0; i != len(next); i++ {
+		c := next[i]
+		v := frees[c]
+		for _, vv := range v {
+			in[vv]--
+			if in[vv] == 0 {
+				next = append(next, vv)
+			}
+		}
+	}
+	return len(next) == n
+}

leetcode/0207.Course-Schedule/207. Course Schedule_test.go

@@ -0,0 +1,48 @@
+package leetcode
+
+import (
+	"fmt"
+	"testing"
+)
+
+type question207 struct {
+	para207
+	ans207
+}
+
+// para 是参数
+// one 代表第一个参数
+type para207 struct {
+	one int
+	pre [][]int
+}
+
+// ans 是答案
+// one 代表第一个答案
+type ans207 struct {
+	one bool
+}
+
+func Test_Problem207(t *testing.T) {
+
+	qs := []question207{
+
+		question207{
+			para207{2, [][]int{[]int{1, 0}}},
+			ans207{true},
+		},
+
+		question207{
+			para207{2, [][]int{[]int{1, 0}, []int{0, 1}}},
+			ans207{false},
+		},
+	}
+
+	fmt.Printf("------------------------Leetcode Problem 207------------------------\n")
+
+	for _, q := range qs {
+		_, p := q.ans207, q.para207
+		fmt.Printf("【input】:%v       【output】:%v\n", p, canFinish(p.one, p.pre))
+	}
+	fmt.Printf("\n\n\n")
+}

leetcode/0207.Course-Schedule/README.md

@@ -0,0 +1,46 @@
+# [207. Course Schedule](https://leetcode.com/problems/course-schedule/)
+
+## 题目
+
+There are a total of n courses you have to take, labeled from `0` to `n-1`.
+
+Some courses may have prerequisites, for example to take course 0 you have to first take course 1, which is expressed as a pair: `[0,1]`
+
+Given the total number of courses and a list of prerequisite **pairs**, is it possible for you to finish all courses?
+
+**Example 1:**
+
+    Input: 2, [[1,0]] 
+    Output: true
+    Explanation: There are a total of 2 courses to take. 
+                 To take course 1 you should have finished course 0. So it is possible.
+
+**Example 2:**
+
+    Input: 2, [[1,0],[0,1]]
+    Output: false
+    Explanation: There are a total of 2 courses to take. 
+                 To take course 1 you should have finished course 0, and to take course 0 you should
+                 also have finished course 1. So it is impossible.
+
+**Note:**
+
+1. The input prerequisites is a graph represented by **a list of edges**, not adjacency matrices. Read more about [how a graph is represented](https://www.khanacademy.org/computing/computer-science/algorithms/graph-representation/a/representing-graphs).
+2. You may assume that there are no duplicate edges in the input prerequisites.
+
+
+## 题目大意
+
+现在你总共有 n 门课需要选，记为 0 到 n-1。在选修某些课程之前需要一些先修课程。 例如，想要学习课程 0 ，你需要先完成课程 1 ，我们用一个匹配来表示他们: [0,1]。给定课程总量以及它们的先决条件，判断是否可能完成所有课程的学习？
+
+
+
+## 解题思路
+
+- 给出 n 个任务，每两个任务之间有相互依赖关系，比如 A 任务一定要在 B 任务之前完成才行。问是否可以完成所有任务。
+- 这一题就是标准的 AOV 网的拓扑排序问题。拓扑排序问题的解决办法是主要是循环执行以下两步，直到不存在入度为0的顶点为止。
+    - 1.  选择一个入度为0的顶点并输出之；
+    - 2. 从网中删除此顶点及所有出边。
+
+    循环结束后，若输出的顶点数小于网中的顶点数，则输出“有回路”信息，即无法完成所有任务；否则输出的顶点序列就是一种拓扑序列，即可以完成所有任务。
+