|
| 1 | +/** |
| 2 | + * res.js |
| 3 | + * @authors Joe Jiang (hijiangtao@gmail.com) |
| 4 | + * @date 2017年04月17日 00:09:34 |
| 5 | + * |
| 6 | + * There are a total of n courses you have to take, labeled from 0 to n - 1. |
| 7 | + * |
| 8 | + * 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] |
| 9 | + * |
| 10 | + * Given the total number of courses and a list of prerequisite pairs, is it possible for you to finish all courses? |
| 11 | + * |
| 12 | + * For example: |
| 13 | + * |
| 14 | + * 2, [[1,0]] |
| 15 | + * There are a total of 2 courses to take. To take course 1 you should have finished course 0. So it is possible. |
| 16 | + * |
| 17 | + * 2, [[1,0],[0,1]] |
| 18 | + * 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. |
| 19 | + * |
| 20 | + * @param {number} numCourses |
| 21 | + * @param {number[][]} prerequisites |
| 22 | + * @return {boolean} |
| 23 | + */ |
| 24 | +let canFinish = function(numCourses, prerequisites) { |
| 25 | + let prelen = prerequisites.length, |
| 26 | + maxNoCircle = numCourses * (numCourses - 1) / 2; |
| 27 | + if (!prelen) { |
| 28 | + return true; |
| 29 | + } else if (prelen > maxNoCircle) { |
| 30 | + return false; |
| 31 | + } |
| 32 | + |
| 33 | + let flags = [], // 存储未访问节点 |
| 34 | + nodemarks = new Array(numCourses), // 存储node访问标记 |
| 35 | + edges = new Array(numCourses); // 存储连边信息 |
| 36 | + for (let i = 0; i < numCourses; i++) { |
| 37 | + flags.push(i); |
| 38 | + nodemarks[i] = 0; |
| 39 | + edges[i] = []; |
| 40 | + } |
| 41 | + |
| 42 | + for (let i = 0; i < prelen; i++) { |
| 43 | + let source = prerequisites[i][0], |
| 44 | + target = prerequisites[i][1]; |
| 45 | + |
| 46 | + edges[target].push(source); |
| 47 | + } |
| 48 | + |
| 49 | + while (flags.length) { |
| 50 | + let node = flags[flags.length - 1]; |
| 51 | + if (!dfsVisit(node)) { |
| 52 | + return false; |
| 53 | + } |
| 54 | + flags.pop(); |
| 55 | + } |
| 56 | + |
| 57 | + return true; |
| 58 | + |
| 59 | + function dfsVisit(node) { |
| 60 | + if (nodemarks[node]) { |
| 61 | + return false; |
| 62 | + } |
| 63 | + |
| 64 | + if (flags.indexOf(node) !== -1) { |
| 65 | + nodemarks[node] = 1; |
| 66 | + let elen = edges[node].length; |
| 67 | + for (let i = 0; i < elen; i++) { |
| 68 | + if (!dfsVisit(edges[node][i])) { |
| 69 | + return false; |
| 70 | + } |
| 71 | + } |
| 72 | + nodemarks[node] = 0; |
| 73 | + } |
| 74 | + |
| 75 | + return true; |
| 76 | + } |
| 77 | +}; |
0 commit comments