linked list

Author: anduo

imgs/subsets.png

@@ -277,3 +277,23 @@ doc中有好几份文档，比较经典，可以参考。
 - substring with concatenation of all words
 - letter combination of a phone number
 
+## chapter05 linked list
+
+需要掌握的技能
+- insert a node in sorted list
+- **remove a node from linked list**
+- **reverse a linked list**
+- merge two linked list
+- find the middle of a linked list
+
+**Dummy Node**
+1. remove duplicates from sorted list i,ii
+2. merge two sorted lists
+3. partition list
+4. reverse linked list ii
+
+**Two Pointer **
+
+## chapter06 dynamic programming
+
+DP的本质就是 **记忆化搜索**

readme.md

@@ -0,0 +1,53 @@
+package ninechapter.ch05_linked_list;
+
+import entity.ListNode;
+
+/**
+ * Created by anduo on 17-3-14.
+ */
+public class Question01SortList {
+    public ListNode sortList(ListNode head) {
+        // merge sort
+        if (head == null || head.next == null) {
+            return head;
+        }
+        ListNode mid = findMiddle(head);
+
+        ListNode right = sortList(mid.next);
+        mid.next = null;
+        ListNode left = sortList(head);
+        return merge(left, right);
+    }
+
+    private ListNode findMiddle(ListNode head) {
+        ListNode slow = head, fast = head.next;
+        while (fast != null && fast.next != null) {
+            fast = fast.next.next;
+            slow = slow.next;
+        }
+        return slow;
+    }
+
+    private ListNode merge(ListNode head1, ListNode head2) {
+        ListNode dummy = new ListNode(0);
+        ListNode tail = dummy;
+        while (head1 != null && head2 != null) {
+            if (head1.val < head2.val) {
+                tail.next = head1;
+                head1 = head1.next;
+            } else {
+                tail.next = head2;
+                head2 = head2.next;
+            }
+            tail = tail.next;
+        }
+        if (head1 != null) {
+            tail.next = head1;
+        } else {
+            tail.next = head2;
+        }
+
+        return dummy.next;
+    }
+
+}

src/ninechapter/ch05_linked_list/Question01SortList.java

@@ -0,0 +1,47 @@
+package ninechapter.ch05_linked_list;
+
+import entity.ListNode;
+
+// https://leetcode.com/problems/reverse-linked-list-ii
+// Reverse a linked list from position m to n. Do it in-place and in one-pass.
+// For example:
+// Given 1->2->3->4->5->NULL, m = 2 and n = 4,
+// return 1->4->3->2->5->NULL.
+
+/**
+ * Created by anduo on 17-3-14.
+ */
+public class Question02ReverseLinkedListII {
+    public ListNode reverseBetween(ListNode head, int m, int n) {
+        if (head == null || m >= n) {
+            return head;
+        }
+
+        ListNode dummy = new ListNode(0);
+
+        // move to m'th node
+        for (int i = 0; i < m; i++) {
+            if (head == null) {
+                return null;
+            }
+            head = head.next;
+        }
+
+        ListNode premNode = head;
+        ListNode mNode = head.next;
+        ListNode nNode = mNode, postnNode = mNode.next;
+        for (int i = m; i < n; i++) {
+            if (postnNode == null) {
+                return null;
+            }
+            ListNode temp = postnNode.next;
+            postnNode.next = nNode;
+            nNode = postnNode;
+            postnNode = temp;
+        }
+        mNode.next = postnNode;
+        premNode.next = nNode;
+
+        return dummy.next;
+    }
+}

src/ninechapter/ch05_linked_list/Question02ReverseLinkedListII.java

@@ -0,0 +1,73 @@
+package ninechapter.ch05_linked_list;
+
+// https://leetcode.com/problems/reorder-list/
+//Given a singly linked list
+// L: L0→L1→…→Ln-1→Ln,
+// reorder it to:
+// L0→Ln→L1→Ln-1→L2→Ln-2→…
+//
+// You must do this in-place without altering the nodes' values.
+//
+// For example,
+// Given {1,2,3,4}, reorder it to {1,4,2,3}.
+
+import entity.ListNode;
+
+/**
+ * Created by anduo on 17-3-14.
+ */
+public class Question03ReorderList {
+
+    private ListNode reverse(ListNode head) {
+        ListNode newHead = null;
+        while (head != null) {
+            ListNode temp = head.next;
+            head.next = newHead;
+            newHead = head;
+            head = temp;
+        }
+        return newHead;
+    }
+
+    private void merge(ListNode head1, ListNode head2) {
+        int index = 0;
+        ListNode dummy = new ListNode(0);
+        while (head1 != null && head2 != null) {
+            if (index % 2 == 0) {
+                dummy.next = head1;
+                head1 = head1.next;
+            } else {
+                dummy.next = head2;
+                head2 = head2.next;
+            }
+            dummy = dummy.next;
+            index++;
+        }
+        if (head1 != null) {
+            dummy.next = head1;
+        } else {
+            dummy.next = head2;
+        }
+    }
+
+    private ListNode findMiddle(ListNode head) {
+        ListNode slow = head, fast = head.next;
+        while (fast != null && fast.next != null) {
+            fast = fast.next.next;
+            slow = slow.next;
+        }
+        return slow;
+    }
+
+    public void reorderList(ListNode head) {
+        if (head == null || head.next == null) {
+            return;
+        }
+
+        ListNode mid = findMiddle(head);// 找到中间节点
+        ListNode tail = reverse(mid.next);// 翻转后半部分链表
+        mid.next = null;// 断开前半部分的链表
+
+        merge(head, tail); // 合并
+    }
+}

src/ninechapter/ch05_linked_list/Question03ReorderList.java

@@ -0,0 +1,44 @@
+package ninechapter.ch05_linked_list;
+
+// https://leetcode.com/problems/partition-list
+// Given a linked list and a value x, partition it such that all nodes less than x come before nodes greater than or equal to x.
+
+// You should preserve the original relative order of the nodes in each of the two partitions.
+//
+// For example,
+// Given 1->4->3->2->5->2 and x = 3,
+// return 1->2->2->4->3->5.
+
+import entity.ListNode;
+
+/**
+ * Created by anduo on 17-3-14.
+ */
+public class Question04PartitionList {
+
+    public ListNode partition(ListNode head, int x) {
+        if (head == null) {
+            return head;
+        }
+
+        ListNode leftDummy = new ListNode(0);
+        ListNode rightDummy = new ListNode(0);
+
+        ListNode left = leftDummy, right = rightDummy;
+        while (head != null) {
+            if (head.val < x) {
+                left.next = head;
+                left = left.next;
+            }else {
+                right.next = head;
+                right = right.next;
+            }
+            head = head.next;
+        }
+
+        right.next = null;
+        left.next = rightDummy.next;
+        return leftDummy.next;
+    }
+
+}

src/ninechapter/ch05_linked_list/Question04PartitionList.java

@@ -0,0 +1,30 @@
+package ninechapter.ch05_linked_list;
+
+import entity.ListNode;
+// https://leetcode.com/problems/linked-list-cycle
+// 判断一个链表是不是有环
+// 快慢指针就可以了
+
+/**
+ * Created by anduo on 17-3-14.
+ */
+public class Question05LinkedListCycle {
+
+    public boolean hasCycle(ListNode head) {
+        if (head == null || head.next == null) {
+            return false;
+        }
+
+        ListNode slow = head, fast = head.next;
+        do {
+            if (fast.next == null || fast.next.next == null) {
+                return false;
+            }
+            fast = fast.next.next;
+            slow = slow.next;
+        } while (slow != fast);
+
+        return true;
+    }
+
+}

src/ninechapter/ch05_linked_list/Question05LinkedListCycle.java

@@ -0,0 +1,37 @@
+package ninechapter.ch05_linked_list;
+
+import entity.ListNode;
+// https://leetcode.com/problems/linked-list-cycle
+// 判断一个链表是不是有环
+// 快慢指针就可以了
+
+/**
+ * Created by anduo on 17-3-14.
+ */
+public class Question06LinkedListCycleII {
+
+    public ListNode detectCycle(ListNode head) {
+        if (head == null || head.next == null) {
+            return null;
+        }
+
+        ListNode fast, slow;
+        fast = head.next;
+        slow = head;
+        while (fast != slow) {// fast追上slow
+            if (fast == null || fast.next == null) {
+                return null;
+            }
+            fast = fast.next.next;
+            slow = slow.next;
+        }
+
+        while (head != slow.next) {
+            // 另一个指针开始从头开始走，slow和head相遇的是否就是环的起点
+            head = head.next;
+            slow = slow.next;
+        }
+        return head;
+    }
+
+}

src/ninechapter/ch05_linked_list/Question06LinkedListCycleII.java

@@ -0,0 +1,71 @@
+package ninechapter.ch05_linked_list;
+
+// https://leetcode.com/problems/copy-list-with-random-pointer/#/description
+// A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.
+//
+// Return a deep copy of the list.
+
+import entity.RandomListNode;
+
+/**
+ * Created by anduo on 17-3-14.
+ */
+///**
+// * Definition for singly-linked list with a random pointer.
+// * class RandomListNode {
+// *     int label;
+// *     RandomListNode next, random;
+// *     RandomListNode(int x) { this.label = x; }
+// * };
+// */
+
+/**
+ * 第一遍扫的时候巧妙运用next指针， 开始数组是1->2->3->4  。
+ * 然后扫描过程中 先建立copy节点 1->1`->2->2`->3->3`->4->4`,
+ * 然后第二遍copy的时候去建立边的copy， 拆分节点, 一边扫描一边拆成两个链表，这里用到两个dummy node。
+ * 第一个链表变回  1->2->3 , 然后第二变成 1`->2`->3`
+ */
+public class Question07CopyListWithRandomPointer {
+
+
+    private void copyNext(RandomListNode head) {
+        while (head != null) {
+            RandomListNode newNode = new RandomListNode(head.label);
+            newNode.random = head.random;
+            newNode.next = head.next;
+            head.next = newNode;
+            head = head.next.next;
+        }
+    }
+
+    private void copyRandom(RandomListNode head) {
+        while (head != null) {
+            if (head.next.random != null) {
+                head.next.random = head.random.next;
+            }
+            head = head.next.next;
+        }
+    }
+
+    private RandomListNode splitList(RandomListNode head) {
+        RandomListNode newHead = head.next;
+        while (head != null) {
+            RandomListNode temp = head.next;
+            head.next = temp.next;
+            head = head.next;
+            if (temp.next != null) {
+                temp.next = temp.next.next;
+            }
+        }
+        return newHead;
+    }
+
+    public RandomListNode copyRandomList(RandomListNode head) {
+        if (head == null) {
+            return null;
+        }
+        copyNext(head);
+        copyRandom(head);
+        return splitList(head);
+    }
+}