Solved Binary Tree Level Order Traversal and Course Schedule

Problem1.cs

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+// Time Complexity : O(n)
+// Space Complexity : O(Width of tree) = Maximum size of elements that can be present in the queue
+// Did this code successfully run on Leetcode : Yes
+// Any problem you faced while coding this : No
+
+
+// Your code here along with comments explaining your approach
+
+/*
+    If root is null I return the resultant list of integer lists as it is. If not, I enqueue the root node to a queue. I iterate through the tree nodes while the queue is not empty for i = size of 
+    queue times. This allows me to distinguish between levels of the tree. For each node in the queue, I dequeue it and add it's value to the temp list. If it has any left or right child, I add them
+    to the queue. At the end of the inner for loop, I add the temporary list to the final resultant list.
+*/
+
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     public int val;
+ *     public TreeNode left;
+ *     public TreeNode right;
+ *     public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+public class Solution
+{
+    public IList<IList<int>> LevelOrder(TreeNode root)
+    {
+        List<IList<int>> result = new();
+
+        if (root == null)
+        {
+            return result;
+        }
+
+        Queue<TreeNode> q = new();
+
+        q.Enqueue(root);
+
+        while (q.Count > 0)
+        {
+            int size = q.Count;
+
+            List<int> tempList = new();
+
+            for (int i = 0; i < size; i++)
+            {
+                TreeNode temp = q.Dequeue();
+                tempList.Add(temp.val);
+
+                if (temp.left != null)
+                {
+                    q.Enqueue(temp.left);
+                }
+
+                if (temp.right != null)
+                {
+                    q.Enqueue(temp.right);
+                }
+            }
+
+            result.Add(tempList);
+        }
+
+        return result;
+    }
+}

Problem2.cs

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+// Time Complexity : O(m+n)
+// Space Complexity : O(m+n)
+// Did this code successfully run on Leetcode : Yes
+// Any problem you faced while coding this : No
+
+
+// Your code here along with comments explaining your approach
+
+/*
+
+*/
+
+public class Solution {
+    public bool CanFinish(int numCourses, int[][] prerequisites) {
+        int count = 0;
+        Dictionary<int, List<int>> adjMap = new();
+        int[] inwardCount = new int[numCourses];
+
+        foreach(int[] prereq in prerequisites)
+        {
+            inwardCount[prereq[1]] += 1;
+
+            if(!adjMap.ContainsKey(prereq[0]))
+            {
+                adjMap[prereq[0]] = new List<int>();
+            }
+
+            adjMap[prereq[0]].Add(prereq[1]);
+        }
+
+        Queue<int> q = new();
+
+        for(int i = 0; i < inwardCount.Length; i++)
+        {
+            if(inwardCount[i] == 0)
+            {
+                q.Enqueue(i);
+                count += 1;
+            }
+        }
+
+        if(q.Count == 0)
+        {
+            return false;
+        }
+
+        while(q.Count != 0)
+        {
+            int currentCourse = q.Dequeue();
+
+            if(adjMap.ContainsKey(currentCourse))
+            {
+                List<int> nextCourses = adjMap[currentCourse];
+
+                foreach(int course in nextCourses)
+                {
+                    inwardCount[course] -= 1;
+                    if(inwardCount[course] == 0)
+                    {
+                        q.Enqueue(course);
+                        count += 1;
+                    }
+                }
+            }
+
+        }
+
+        return count == numCourses;
+    }
+}