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Commit 47515b9

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Add solution for Course Schedule II
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‎README.md

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@@ -147,6 +147,7 @@ Algorithm exercises from LeetCode implemented in Java v11.
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### Topological Sort
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- Course Schedule | [Problem](https://leetcode.com/problems/course-schedule) | [Solution](src/solutions/CourseSchedule.java)
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- Course Schedule II | [Problem](https://https://leetcode.com/problems/course-schedule-ii) | [Solution](src/solutions/CourseScheduleII.java)
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- Find All Possible Recipes from Given Supplies | [Problem](https://leetcode.com/problems/find-all-possible-recipes-from-given-supplies) | [Solution](src/solutions/FindAllPossibleRecipes.java)
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### Bit Manipulation

‎src/solutions/CourseScheduleII.java

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package solutions;
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import java.util.*;
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// [Problem] https://leetcode.com/problems/course-schedule-ii
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class CourseScheduleII {
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// Topological sort
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// O(v + e) time, O(v + e) space
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// where v = number of courses, e = number of prerequisites
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public int[] findOrder(int numCourses, int[][] prerequisites) {
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Map<Integer, List<Integer>> nextCourseMap = new HashMap<>();
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int[] numPrerequisites = new int[numCourses];
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for (int[] courseToPrerequisite : prerequisites) {
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int course = courseToPrerequisite[0];
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int prerequisite = courseToPrerequisite[1];
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nextCourseMap.putIfAbsent(prerequisite, new ArrayList<>());
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nextCourseMap.get(prerequisite).add(course);
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numPrerequisites[course]++;
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}
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Queue<Integer> coursesToTake = new LinkedList<>();
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for (int i = 0; i < numCourses; i++) {
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if (numPrerequisites[i] == 0) {
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coursesToTake.add(i);
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}
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}
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int[] order = new int[numCourses];
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int orderIndex = 0;
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while (!coursesToTake.isEmpty() && orderIndex < numCourses) {
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int currentCourse = coursesToTake.poll();
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order[orderIndex++] = currentCourse;
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List<Integer> nextCourses = nextCourseMap.get(currentCourse);
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if (nextCourses != null) {
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for (int nextCourse : nextCourses) {
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if (--numPrerequisites[nextCourse] == 0) {
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coursesToTake.add(nextCourse);
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}
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}
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}
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}
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return orderIndex == numCourses ? order : new int[0];
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}
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// Test
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public static void main(String[] args) {
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CourseScheduleII solution = new CourseScheduleII();
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int numCourses1 = 2;
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int[][] prerequisites1 = {{1, 0}};
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int[] expectedOutput1 = {0, 1};
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int[] actualOutput1 = solution.findOrder(numCourses1, prerequisites1);
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System.out.println("Test 1 passed? " + Arrays.equals(expectedOutput1, actualOutput1));
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int numCourses2 = 4;
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int[][] prerequisites2 = {{1, 0}, {2, 0}, {3, 1}, {3, 2}};
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int[] expectedOutput2 = {0, 1, 2, 3};
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int[] actualOutput2 = solution.findOrder(numCourses2, prerequisites2);
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System.out.println("Test 2 passed? " + Arrays.equals(expectedOutput2, actualOutput2));
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}
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}

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