添加链表排序算法

董林 · 董林 · commit 53a014364bb5 · 2018-07-06T23:52:01.000+08:00
diff --git a/src/main/java/com/crossoverjie/algorithm/LinkedListMergeSort.java b/src/main/java/com/crossoverjie/algorithm/LinkedListMergeSort.java
@@ -0,0 +1,127 @@
+package com.crossoverjie.algorithm;
+
+/**
+ * 链表排序, 建议使用归并排序
+ *
+ * @author 6563699600@qq.com
+ * @date 6/7/2018 11:42 PM
+ * @since 1.0
+ */
+public class LinkedListMergeSort {
+
+    final static class Node {
+        int e;
+        Node next;
+
+        public Node() {
+        }
+
+        public Node(int e, Node next) {
+            this.e = e;
+            this.next = next;
+        }
+    }
+
+    public Node mergeSort(Node first, int length) {
+
+        if (length == 1) {
+            return first;
+        } else {
+            Node middle = new Node();
+            Node tmp = first;
+
+            /**
+             * 后期会对这里进行优化，通过一次遍历算出长度和中间元素
+             */
+            for (int i = 0; i < length; i++) {
+                if (i == length / 2) {
+                    break;
+                }
+                middle = tmp;
+                tmp = tmp.next;
+            }
+
+            /**
+             *  这里是链表归并时要注意的细节
+             */
+            Node right = middle.next;
+            middle.next = null;
+
+            Node leftStart = mergeSort(first, length / 2);
+            Node rightStart;
+            if (length % 2 == 0) {
+                rightStart = mergeSort(right, length / 2);
+            } else {
+                rightStart = mergeSort(right, length / 2 + 1);
+            }
+            return mergeList(leftStart, rightStart);
+        }
+    }
+
+    public Node mergeList(Node left, Node right) {
+
+        Node head = new Node();
+        Node result = head;
+
+        /**
+         * 思想就是两个链表同时遍历，将更的元素插入结果中，同时更更大的元素所属的链表的指针向下移动
+         */
+        while (!(null == left && null == right)) {
+            Node tmp;
+            if (left == null) {
+                result.next = right;
+                break;
+            } else if (right == null) {
+                result.next = left;
+                break;
+            } else if (left.e >= right.e) {
+                tmp = left;
+                result.next = left;
+                result = tmp;
+                left = left.next;
+            } else {
+                tmp = right;
+                result.next = right;
+                result = tmp;
+                right = right.next;
+            }
+        }
+
+        return head.next;
+    }
+
+    public static void main(String[] args) {
+
+        Node head = new Node();
+
+        head.next = new Node(7,
+                new Node(2,
+                        new Node(5,
+                                new Node(4,
+                                        new Node(3,
+                                                new Node(6,
+                                                        new Node(11, null)
+                                                )
+                                        )
+                                )
+                        )
+                )
+        );
+
+        int length = 0;
+
+        for (Node e = head.next; null != e; e = e.next) {
+            length++;
+        }
+
+
+        LinkedListMergeSort sort = new LinkedListMergeSort();
+        head.next = sort.mergeSort(head.next, length);
+
+
+        for (Node n = head.next; n != null; n = n.next) {
+            System.out.println(n.e);
+        }
+
+    }
+}
