2024/8/21 Hot100 LinkedList

src/main/java/com/cool/hot100/linkedlist/Num141.java

@@ -0,0 +1,31 @@
+package com.cool.hot100.linkedlist;
+
+public class Num141 {
+
+    /**
+     * Date 2024/8/21
+     * DayNumber 1
+     * Hard 1
+     *
+     * @return
+     */
+    public boolean hasCycle(ListNode head) {
+        if (head == null)
+            return false;
+        ListNode fastNode = head.next;
+        ListNode slowNode = head;
+        if (fastNode == null)
+            return false;
+        while (fastNode != null) {
+            if (fastNode.next==null){
+                return false;
+            }
+            fastNode=fastNode.next.next;
+            slowNode = slowNode.next;
+            if (slowNode == fastNode)
+                return true;
+        }
+        return false;
+    }
+
+}

src/main/java/com/cool/hot100/linkedlist/Num142.java

@@ -0,0 +1,64 @@
+package com.cool.hot100.linkedlist;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+public class Num142 {
+
+
+    /**
+     * Date 2024/8/21
+     * DayNumber 2
+     * Hard 2
+     *
+     * @param head
+     * @return
+     */
+    public ListNode detectCycle(ListNode head) {
+
+        // 空间复杂度O(n)
+//        Map<ListNode,Integer> map=new HashMap<>();
+//        while (head!=null){
+//            if(map.containsKey(head)){
+//                return head;
+//            }
+//            map.put(head,map.getOrDefault(head,0)+1);
+//            head=head.next;
+//        }
+//        return null;
+
+        // 空间复杂度O(1)
+        if (head == null) return null;
+        ListNode slow = head;
+        ListNode fast = head;
+        do {
+            if (fast == null || fast.next == null) {
+                return null;
+            }
+            slow = slow.next;
+            fast = fast.next.next;
+        } while (slow != fast);
+        ListNode node = head;
+        while (slow != node) {
+            slow = slow.next;
+            node = node.next;
+        }
+        return node;
+    }
+
+    @Test
+    public void test() {
+//        ListNode node=new ListNode(5,null);
+        ListNode node1 = new ListNode(-4, null);
+        ListNode node2 = new ListNode(0, node1);
+        ListNode node3 = new ListNode(2, node2);
+        ListNode node4 = new ListNode(3, node3);
+        node1.next = node3;
+        detectCycle(node4);
+    }
+
+}

src/main/java/com/cool/hot100/linkedlist/Num21.java

@@ -0,0 +1,54 @@
+package com.cool.hot100.linkedlist;
+
+public class Num21 {
+
+
+    /**
+     * Date 2024/8/21
+     * DayNumber 3
+     * Hard 1
+     *
+     * @param list1
+     * @param list2
+     * @return
+     */
+    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
+        ListNode reNode;
+        if(list1==null||list2==null){
+            return list1==null?list2:list1;
+        }
+        if (list1.val > list2.val) {
+            reNode = list2;
+            list2 = list2.next;
+        } else {
+            reNode = list1;
+            list1 = list1.next;
+        }
+        ListNode returnNode=reNode;
+        while (list1 != null && list2 != null) {
+            if (list1.val > list2.val) {
+                reNode.next = list2;
+                list2 = list2.next;
+                reNode = reNode.next;
+
+            } else {
+                reNode.next = list1;
+                list1 = list1.next;
+                reNode = reNode.next;
+
+            }
+        }
+        while (list1 != null) {
+            reNode.next = list1;
+            list1 = list1.next;
+            reNode = reNode.next;
+        }
+        while (list2 != null) {
+            reNode.next = list2;
+            list2 = list2.next;
+            reNode = reNode.next;
+        }
+        return returnNode;
+    }
+
+}