From 0de9c704086ac159d516064d0f987d852b0e5ea0 Mon Sep 17 00:00:00 2001 From: rwang23 Date: Mon, 18 Jan 2016 01:27:05 -0500 Subject: [PATCH] Convert Binary Search Tree to Doubly Linked List --- ...inary-Search-Tree-to-Doubly-Linked-List.md | 73 +++++++++++++++ Linkedlist/Reorder-List.md | 68 +++++++------- Linkedlist/Sort-List.md | 90 +++++++++++++++++++ SUMMARY.md | 2 + 4 files changed, 198 insertions(+), 35 deletions(-) create mode 100644 Linkedlist/Convert-Binary-Search-Tree-to-Doubly-Linked-List.md diff --git a/Linkedlist/Convert-Binary-Search-Tree-to-Doubly-Linked-List.md b/Linkedlist/Convert-Binary-Search-Tree-to-Doubly-Linked-List.md new file mode 100644 index 0000000..52c61e2 --- /dev/null +++ b/Linkedlist/Convert-Binary-Search-Tree-to-Doubly-Linked-List.md @@ -0,0 +1,73 @@ +##Convert Binary Search Tree to Doubly Linked List + + Convert a binary search tree to doubly linked list with in-order traversal. + + Example + Given a binary search tree: + + 4 + / \ + 2 5 + / \ + 1 3 + return 1<->2<->3<->4<->5 + +####Tags Expand +Linked List + + +####解法 +- 简单的中序遍历 +- 一遍遍历,一遍就输出双向链表 +- 用非递归也是一样 + +```java +/** + * Definition of TreeNode: + * public class TreeNode { + * public int val; + * public TreeNode left, right; + * public TreeNode(int val) { + * this.val = val; + * this.left = this.right = null; + * } + * } + * Definition for Doubly-ListNode. + * public class DoublyListNode { + * int val; + * DoublyListNode next, prev; + * DoublyListNode(int val) { + * this.val = val; + * this.next = this.prev = null; + * } + * } + */ +public class Solution { + /** + * @param root: The root of tree + * @return: the head of doubly list node + */ + DoublyListNode cur = new DoublyListNode(0); + DoublyListNode dummy = cur; + DoublyListNode pre = null; + + public DoublyListNode bstToDoublyList(TreeNode root) { + // Write your code here + if (root == null) { + return null; + } + + bstToDoublyList(root.left); + + cur.next = new DoublyListNode(root.val); + pre = cur; + cur = cur.next; + cur.prev = pre; + + bstToDoublyList(root.right); + + return dummy.next; + } +} + +``` diff --git a/Linkedlist/Reorder-List.md b/Linkedlist/Reorder-List.md index cf6ec18..adf26c5 100644 --- a/Linkedlist/Reorder-List.md +++ b/Linkedlist/Reorder-List.md @@ -15,7 +15,7 @@ ####思路 - 拆分，然后后半段翻转，再merge -- 重做 +- 重做 : 完成 ```java /** @@ -39,51 +39,49 @@ public class Solution { if (head == null || head.next == null) { return; } - ListNode slow = head; + + ListNode dummy = new ListNode(0); + dummy.next = head; ListNode fast = head; - while (fast != null && fast.next != null) { + ListNode slow = head; + + while (fast.next != null && fast.next.next != null) { fast = fast.next.next; slow = slow.next; } - ListNode tail = reverse(slow.next); + + ListNode half = slow.next; slow.next = null; + half = reverseList(half); - int index = 0; - ListNode dummy = new ListNode(0); - ListNode temp = dummy; - while (head!=null && tail != null) { - if (index % 2 == 0) { - dummy.next = head; - head = head.next; - } else { - dummy.next = tail; - tail = tail.next; - } - dummy = dummy.next; - index ++; + while (head != null && half != null) { + ListNode next = head.next; + ListNode secondnext = null; + secondnext = half.next; + head.next = half; + half.next = next; + head = next; + half = secondnext; } - if (head != null) { - dummy.next = head; - } else { - dummy.next = tail; - } - head = temp.next; + } - public ListNode reverse(ListNode head) { - // write your code here - if (head == null ) { - return null; + public ListNode reverseList(ListNode head) { + if (head == null || head.next == null) { + return head; } - ListNode cur = head; - ListNode reverse = null; - while (cur != null) { - ListNode temp = cur.next; - cur.next = reverse; - reverse = cur; - cur = temp; + + //ListNode dummy = new ListNode(0); + ListNode pre = null; + + while (head != null) { + ListNode next = head.next; + head.next = pre; + pre = head; + head = next; } - return reverse; + + return pre; } } diff --git a/Linkedlist/Sort-List.md b/Linkedlist/Sort-List.md index 13e849d..b857cfa 100644 --- a/Linkedlist/Sort-List.md +++ b/Linkedlist/Sort-List.md @@ -83,6 +83,96 @@ public class Solution { } } +``` +####Merge Sort的模板做法 +```java +/** + * Definition for ListNode. + * public class ListNode { + * int val; + * ListNode next; + * ListNode(int val) { + * this.val = val; + * this.next = null; + * } + * } + */ +public class Solution { + /** + * @param head: The head of linked list. + * @return: You should return the head of the sorted linked list, + * using constant space complexity. + */ + public ListNode sortList(ListNode head) { + // write your code here + if (head == null || head.next == null) { + return head; + } + + ListNode mid = findMiddle(head); + ListNode next = mid.next; + mid.next = null; + + return helper(head, next); + } + + public ListNode helper(ListNode headA, ListNode headB) { + if (headB == null) { + return headA; + } + + ListNode mid = findMiddle(headA); + ListNode next = mid.next; + mid.next = null; + ListNode left = helper(headA, next); + + mid = findMiddle(headB); + next = mid.next; + mid.next = null; + ListNode right = helper(headB, next); + + return mergeTwoLists(left, right); + } + + public ListNode mergeTwoLists(ListNode l1, ListNode l2) { + // write your code here + ListNode mergelist = new ListNode(0); + ListNode head = mergelist; + while (true) { + if (l1 == null) { + mergelist.next = l2; + break; + } else if (l2 == null) { + mergelist.next = l1; + break; + } + if (l1.val >= l2.val) { + mergelist.next = l2; + l2 = l2.next; + } else { + mergelist.next = l1; + l1 = l1.next; + } + mergelist = mergelist.next; + } + return head.next; + } + + public ListNode findMiddle(ListNode head) { + if (head == null || head.next == null) { + return head; + } + + ListNode fast = head; + ListNode slow = head; + + while (fast.next != null && fast.next.next != null) { + fast = fast.next.next; + slow = slow.next; + } + return slow; + } +} ``` diff --git a/SUMMARY.md b/SUMMARY.md index 2df0e9b..2de385b 100644 --- a/SUMMARY.md +++ b/SUMMARY.md @@ -149,6 +149,8 @@ This is the summary of my experience in LintCode. * [Reorder List](Linkedlist/Reorder-List.md) * [Copy List With Random Pointer](Linkedlist/Copy-List-with-Random-Pointer.md) * [Convert Sorted List to Binary Search Tree](Linkedlist/Convert-Sorted-List-to-Binary-Search-Tree.md) + * [Convert Binary Search Tree to Doubly Linked List](Linkedlist/Convert-Binary-Search-Tree-to-Doubly-Linked-List.md) + * [Data Structure](DataStructure/README.md) * [String](DataStructure/string.md)