剑指offer-面试题57-删除链表中重复的结点

结点结构定义：

package case57_DeleteDuplicatedListNode;

/**
* 链表的节点结构定义
*
* @author WangSai
*
*/
public class ListNode {

int data;
ListNode next;

public ListNode() {
}

public ListNode(int data) {
this.data = data;
}

}


删除重复节点的代码实现：

package case57_DeleteDuplicatedListNode;

/**
* 题目：在一个排序的链表中，如何删除重复的结点？例如，在下图a中重复节点被删除之后，链表如b图所示。
*
* a: N1 ——————> N2 ——————> N3 ——————> N3 ——————> N4 ——————> N4 ——————> N5
*
* b: N1 ——————> N2 ——————> N5
*
* @author WangSai
*
*/
public class DeleteDuplicatedListNode {

/**
* 设置一个前驱节点，保存当前节点的上一个节点。设置临时头结点，指向原链表的头结点。
*
* @param head，原链表的头结点
* @return 删除重复节点之后的新链表的头结点
*/
private static ListNode myDelete(ListNode head) {
// 异常值处理
if (head == null)
return null;
// 临时头结点
ListNode root = new ListNode();
// 当前节点的前一个节点
ListNode pre = root;
// 当前节点
ListNode cur = head;
root.next = head;

while (cur != null && cur.next != null) {
// 有重复结点，与cur值相同的结点都要删除
if (cur.data == cur.next.data) {
// 找到下一个不同值的节点，注意其有可能也是重复节点
while (cur.next != null && cur.data == cur.next.data) {
cur = cur.next;
}
// 指向下一个节点，prev.next也可能是重复结点
// 所以prev不要移动到下一个结点
pre.next = cur.next;
} else {
pre.next = cur;
pre = pre.next;
}
cur = cur.next;
}
return root.next;
}

/**
* @param args
*/
public static void main(String[] args) {
// 有重复节点，重复节点在中间
test1();
// 有重复节点，重复节点开始部分
test2();
// 所有节点重复
test3();
// 没有重复节点
test4();
}

/**
* 有重复节点，重复节点在中间
*/
public static void test1() {
ListNode head = new ListNode(1);
ListNode n2 = new ListNode(2);
ListNode n3 = new ListNode(3);
ListNode n4 = new ListNode(3);
ListNode n5 = new ListNode(5);
ListNode n6 = new ListNode(6);

head.next = n2;
n2.next = n3;
n3.next = n4;
n4.next = n5;
n5.next = n6;

System.out.println("删除重复节点之前：");
ListNode temp = head;
while (temp != null) {
System.out.print(temp.data + "->");
temp = temp.next;
}
System.out.println();
System.out.println("删除重复节点之后：");
ListNode node = myDelete(head);
while (node != null) {
System.out.print(node.data + "->");
node = node.next;
}
System.out.println();
System.out.println("----------------");
}

/**
* 有重复节点，重复节点开始部分
*/
public static void test2() {
ListNode head = new ListNode(2);
ListNode n2 = new ListNode(2);
ListNode n3 = new ListNode(3);
ListNode n4 = new ListNode(3);
ListNode n5 = new ListNode(5);
ListNode n6 = new ListNode(6);

head.next = n2;
n2.next = n3;
n3.next = n4;
n4.next = n5;
n5.next = n6;

System.out.println("删除重复节点之前：");
ListNode temp = head;
while (temp != null) {
System.out.print(temp.data + "->");
temp = temp.next;
}
System.out.println();
System.out.println("删除重复节点之后：");
ListNode node = myDelete(head);
while (node != null) {
System.out.print(node.data + "->");
node = node.next;
}
System.out.println();
System.out.println("----------------");
}

/**
* 所有节点重复
*/
public static void test3() {
ListNode head = new ListNode(2);
ListNode n2 = new ListNode(2);
ListNode n3 = new ListNode(2);
ListNode n4 = new ListNode(2);
ListNode n5 = new ListNode(2);
ListNode n6 = new ListNode(2);

head.next = n2;
n2.next = n3;
n3.next = n4;
n4.next = n5;
n5.next = n6;

System.out.println("删除重复节点之前：");
ListNode temp = head;
while (temp != null) {
System.out.print(temp.data + "->");
temp = temp.next;
}
System.out.println();
System.out.println("删除重复节点之后：");
ListNode node = myDelete(head);
while (node != null) {
System.out.print(node.data + "->");
node = node.next;
}
System.out.println();
System.out.println("----------------");
}

/**
* 没有节点重复
*/
public static void test4() {
ListNode head = new ListNode(1);
ListNode n2 = new ListNode(2);
ListNode n3 = new ListNode(3);
ListNode n4 = new ListNode(4);
ListNode n5 = new ListNode(5);
ListNode n6 = new ListNode(6);

head.next = n2;
n2.next = n3;
n3.next = n4;
n4.next = n5;
n5.next = n6;

System.out.println("删除重复节点之前：");
ListNode temp = head;
while (temp != null) {
System.out.print(temp.data + "->");
temp = temp.next;
}
System.out.println();
System.out.println("删除重复节点之后：");
ListNode node = myDelete(head);
while (node != null) {
System.out.print(node.data + "->");
node = node.next;
}
System.out.println();
System.out.println("----------------");
}
}