[sora0319] Week 10 Solutions

course-schedule/sora0319.java

@@ -0,0 +1,47 @@
+public class Solution {
+    public boolean canFinish(int numCourses, int[][] prerequisites) {
+        int[] degree = new int[numCourses];
+
+        Map<Integer, List<Integer>> graph = new HashMap<>();
+
+        for (int[] p : prerequisites) {
+            int course = p[0];
+            int pre = p[1];
+
+            degree[course]++;
+
+            if (!graph.containsKey(pre)) {
+                graph.put(pre, new ArrayList<>());
+            }
+            graph.get(pre).add(course);
+        }
+
+        Queue<Integer> q = new LinkedList<>();
+        for (int i = 0; i < numCourses; i++) {
+            if (degree[i] == 0) {
+                q.offer(i);
+            }
+        }
+
+        int finishedCourses = 0;
+
+        while (!q.isEmpty()) {
+            int curr = q.poll();
+            finishedCourses++;
+
+            if (graph.containsKey(curr)) {
+                for (int neighbor : graph.get(curr)) {
+                    degree[neighbor]--;
+                    if (degree[neighbor] == 0) {
+                        q.offer(neighbor);
+                    }
+                }
+            }
+        }
+
+        if(finishedCourses == numCourses) return true;
+
+        return false;
+    }
+}
+

invert-binary-tree/sora0319.java

@@ -0,0 +1,15 @@
+public class Solution {
+    public TreeNode invertTree(TreeNode root) {
+        if (root == null) {
+            return null;
+        }
+
+        TreeNode left = invertTree(root.left);
+        TreeNode right = invertTree(root.right);
+
+        root.left = right;
+        root.right = left;
+
+        return root;
+    }
+}

jump-game/sora0319.java

@@ -0,0 +1,11 @@
+public class Solution {
+    public boolean canJump(int[] nums) {
+        int longLength = 0;
+        for (int i = 0; i < nums.length; i++) {
+            if (i > longLength) return false;
+            longLength = Math.max(longLength, i + nums[i]);
+        }
+        return true;
+    }
+}
+

merge-k-sorted-lists/sora0319.java

@@ -0,0 +1,26 @@
+public class Solution {
+    public ListNode mergeKLists(ListNode[] lists) {
+        PriorityQueue<ListNode> pq = new PriorityQueue<>(Comparator.comparingInt(node -> node.val));
+
+        for (ListNode list : lists) {
+            if (list != null) {
+                pq.offer(list);
+            }
+        }
+
+        ListNode temp = new ListNode(-1);
+        ListNode head = temp;
+
+        while (!pq.isEmpty()) {
+            ListNode minNode = pq.poll();
+            head.next = minNode;
+            head = head.next;
+
+            if (minNode.next != null) {
+                pq.offer(minNode.next);
+            }
+        }
+
+        return temp.next;
+    }
+}

search-in-rotated-sorted-array/sora0319.java

@@ -0,0 +1,51 @@
+public class Solution {
+    public int search(int[] nums, int target) {
+        int p = findPivot(nums);
+
+        int index = binarySearch(nums, 0, p - 1, target);
+        if (index != -1) {
+            return index;
+        }
+        return binarySearch(nums, p, nums.length - 1, target);
+    }
+
+    private int findPivot(int[] nums) {
+        int l = 0;
+        int h = nums.length - 1;
+
+        while (l <= h) {
+            int mid = l + (h - l) / 2;
+
+            if (mid > 0 && nums[mid - 1] > nums[mid]) {
+                return mid;
+            }
+
+            if (nums[0] <= nums[mid]) {
+                l = mid + 1;
+            } else {
+                h = mid - 1;
+            }
+        }
+
+        return 0;
+    }
+
+    private int binarySearch(int[] nums, int l, int h, int target) {
+        while (l <= h) {
+            int mid = l + (h - l) / 2;
+
+            if (nums[mid] == target) {
+                return mid;
+            }
+
+            if (nums[mid] < target) {
+                l = mid + 1;
+            } else {
+                h = mid - 1;
+            }
+        }
+
+        return -1;
+    }
+}
+