zoukankan      html  css  js  c++  java
  • LeetCode-Course Schedule II

    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, return the ordering of courses you should take to finish all courses.

    There may be multiple correct orders, you just need to return one of them. If it is impossible to finish all courses, return an empty array.

    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 the correct course order is [0,1]

    4, [[1,0],[2,0],[3,1],[3,2]]

    There are a total of 4 courses to take. To take course 3 you should have finished both courses 1 and 2. Both courses 1 and 2 should be taken after you finished course 0. So one correct course order is [0,1,2,3]. Another correct ordering is[0,2,1,3].

    Note:
    The input prerequisites is a graph represented by a list of edges, not adjacency matrices. Read more about how a graph is represented.

    Solution:

     1 public class Solution {
     2     public int[] findOrder(int numCourses, int[][] prerequisites) {
     3         if (numCourses ==0)
     4             return new int[0];
     5 
     6         int[] preNum = new int[numCourses];
     7         List<List<Integer>> childMap = new ArrayList<List<Integer>>();
     8         for (int i=0;i<numCourses;i++){
     9             childMap.add(new ArrayList<Integer>());
    10         }
    11         
    12         for (int[] pair : prerequisites) {
    13             int course1 = pair[0], course2 = pair[1];
    14             preNum[course1]++;
    15             childMap.get(course2).add(course1);
    16         }
    17 
    18         // Get init list
    19         Queue<Integer> courseList = new LinkedList<Integer>();
    20         for (int i = 0; i < numCourses; i++)
    21             if (preNum[i] == 0) {
    22                 courseList.add(i);
    23             }
    24 
    25         int[] resList = new int[numCourses];
    26         int index = 0;
    27         while (!courseList.isEmpty()) {
    28             int course1 = courseList.poll();
    29             resList[index++] = course1;
    30             List<Integer> childs = childMap.get(course1);
    31             for (int course2 : childs) {
    32                 preNum[course2]--;
    33                 if (preNum[course2] == 0) {
    34                     courseList.add(course2);
    35                 }
    36             }
    37         }
    38 
    39         if (index != numCourses) return new int[0];
    40         return resList;
    41     }
    42 }
  • 相关阅读:
    鼠标移动,背景变色
    datatable 删除行
    GridView新增一行,更新所有行實現
    让层垂直居中于浏览器窗口
    extjs学习笔记(转)
    Extjs中的panel
    JDK和JRE的区别(转)
    EXTJS中form添加按钮触发事件
    web.xml详解
    Oracle数据库中的诊断文件(转)
  • 原文地址:https://www.cnblogs.com/lishiblog/p/5820423.html
Copyright © 2011-2022 走看看