package com.test;

import com.test.ListNode;

import java.util.Stack;

/**
 * Created by Demrystv.
 */
public class RemoveListNodeOfValue {


    /**
     * 方法一，使用栈或者其他容器收集节点的方法，其时间复杂度是 O(N)，空间复杂度是O(N)
     */
    public ListNode removeValue1(ListNode head, int num) {
        Stack<ListNode> stack = new Stack<ListNode>();
        while (head != null) {
            if (head.val != num) {
                stack.push(head);
            }
            head = head.next;
        }
        while (!stack.isEmpty()) {
            stack.peek().next = head;
            head = stack.pop();
        }
        return head;
    }
    
    
    /**
     *方法二，不使用任何容器，直接调整的方法，其时间复杂度是 O(N)，空间复杂度是O(1)
     */
    public ListNode removeValue2(ListNode head, int num){
        while (head != null){
            if (head.val != num){
                break;
            }
            head = head.next;
        }
        ListNode pre = head;
        ListNode cur = head;
        while (cur != null){
            if (cur.val == num){
                pre.next = cur.next;
            }else {
                pre = cur;
            }
            cur = cur.next;
        }
        return head;
    }
    
    
}