add: Course Schedule

Author: hijiangtao

README.md

@@ -49,6 +49,7 @@ This is the solutions collection of my LeetCode submissions, most of them are pr
 |196|[Delete Duplicate Emails](https://leetcode.com/problems/delete-duplicate-emails/) | [SQL](./src/delete-duplicate-emails/res.txt)|Easy|
 |197|[Rising Temperature](https://leetcode.com/problems/rising-temperature/) | [SQL](./src/rising-temperature/res.txt)|Easy|
 |206|[Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/) | [JavaScript](./src/reverse-linked-list/res.js)|Easy|
+|207|[Course Schedule](https://leetcode.com/problems/course-schedule/) | [JavaScript](./src/course-schedule/res.js)|Medium|
 |240|[Search a 2D Matrix II](https://leetcode.com/problems/search-a-2d-matrix-ii/) | [JavaScript](./src/search-a-2d-matrix-ii/res.js)|Medium|
 |307|[Range Sum Query - Mutable](https://leetcode.com/problems/range-sum-query-mutable/) | [JavaScript](./src/range-sum-query-mutable/res.js)|Medium|
 |342|[Power of Four](https://leetcode.com/problems/power-of-four/) | [JavaScript](./src/power-of-four/res.js)|Easy|

src/course-schedule/res.js

@@ -0,0 +1,77 @@
+/**
+ * res.js
+ * @authors Joe Jiang ([email protected])
+ * @date    2017-04-17 00:09:34
+ * 
+ * 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?
+ * 
+ * For example:
+ * 
+ * 2, [[1,0]]
+ * There are a total of 2 courses to take. To take course 1 you should have finished course 0. So it is possible.
+ * 
+ * 2, [[1,0],[0,1]]
+ * 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.
+ * 
+ * @param {number} numCourses
+ * @param {number[][]} prerequisites
+ * @return {boolean}
+ */
+let canFinish = function(numCourses, prerequisites) {
+    let prelen = prerequisites.length,
+        maxNoCircle = numCourses * (numCourses - 1) / 2;
+    if (!prelen) {
+        return true;
+    } else if (prelen > maxNoCircle) {
+        return false;
+    }
+
+    let flags = [], // 存储未访问节点
+        nodemarks = new Array(numCourses), // 存储node访问标记
+        edges = new Array(numCourses); // 存储连边信息
+    for (let i = 0; i < numCourses; i++) {
+        flags.push(i);
+        nodemarks[i] = 0;
+        edges[i] = [];
+    }
+
+    for (let i = 0; i < prelen; i++) {
+        let source = prerequisites[i][0],
+            target = prerequisites[i][1];
+
+        edges[target].push(source);
+    }
+
+    while (flags.length) {
+        let node = flags[flags.length - 1];
+        if (!dfsVisit(node)) {
+            return false;
+        }
+        flags.pop();
+    }
+
+    return true;
+
+    function dfsVisit(node) {
+        if (nodemarks[node]) {
+            return false;
+        }
+
+        if (flags.indexOf(node) !== -1) {
+            nodemarks[node] = 1;
+            let elen = edges[node].length;
+            for (let i = 0; i < elen; i++) {
+                if (!dfsVisit(edges[node][i])) {
+                    return false;
+                }
+            }
+            nodemarks[node] = 0;
+        }
+
+        return true;
+    }
+};