课程表 II

Author: mayuanucas

README.md

@@ -96,6 +96,7 @@
 | 206 | 链表 | [反转链表](src/main/java/algorithm/leetcode/Solution206.java) | 简单 |
 | 207 | 深度优先搜索、广度优先搜索、图、拓扑排序 | [课程表](src/main/java/algorithm/leetcode/Solution207.java) | 中等 |
 | 209 | 数组、双指针、二分查找 | [长度最小的子数组](src/main/java/algorithm/leetcode/Solution209.java) | 中等 |
+| 210 | 深度优先搜索、广度优先搜索、图、拓扑排序 | [课程表 II](src/main/java/algorithm/leetcode/Solution210.java) | 中等 |
 | 211 | 设计、字典数、回溯算法 | [添加与搜索单词 - 数据结构设计](src/main/java/algorithm/leetcode/Solution211.java) | 中等 |
 | 212 | 字典数、回溯算法 | [单词搜索 II](src/main/java/algorithm/leetcode/Solution212.java) | 困难 |
 | 213 | 动态规划 | [打家劫舍 II](src/main/java/algorithm/leetcode/Solution213.java) | 中等 |

src/main/java/algorithm/leetcode/Solution210.java

@@ -0,0 +1,51 @@
+package algorithm.leetcode;
+
+import java.util.LinkedList;
+import java.util.Queue;
+
+/**
+ * @author: mayuan
+ * @desc: 课程表 II
+ * @date: 2019/03/13
+ */
+public class Solution210 {
+ public int[] findOrder(int numCourses, int[][] prerequisites) {
+ if (numCourses == 0) {
+ return null;
+ }
+ // Convert graph presentation from edges to indegree of adjacent list.
+ int[] indegree = new int[numCourses];
+ int[] order = new int[numCourses];
+ int index = 0;
+ // Indegree - how many prerequisites are needed.
+ for (int i = 0; i < prerequisites.length; i++) {
+ indegree[prerequisites[i][0]]++;
+ }
+
+ Queue<Integer> queue = new LinkedList<Integer>();
+ for (int i = 0; i < numCourses; i++) {
+ if (indegree[i] == 0) {
+ // Add the course to the order because it has no prerequisites.
+ order[index++] = i;
+ queue.offer(i);
+ }
+ }
+ // How many courses don't need prerequisites.
+ while (!queue.isEmpty()) {
+ // Already finished this prerequisite course.
+ int prerequisite = queue.poll();
+ for (int i = 0; i < prerequisites.length; i++) {
+ if (prerequisites[i][1] == prerequisite) {
+ indegree[prerequisites[i][0]]--;
+ if (indegree[prerequisites[i][0]] == 0) {
+ // If indegree is zero, then add the course to the order.
+ order[index++] = prerequisites[i][0];
+ queue.offer(prerequisites[i][0]);
+ }
+ }
+ }
+ }
+
+ return (index == numCourses) ? order : new int[0];
+ }
+}