17.在單鏈表中刪除指定值的節點

【題目】

給定一個鏈表的頭節點head和一個整數num，請實現函數將值爲num的節點全部刪除

【代碼1】

時間複雜度O(n)，空間複雜度O(n)

class Solution {
    public ListNode deleteNode(ListNode head, int val) {
        ListNode cur = head;
        Stack<ListNode> stack = new Stack<>();
        while(cur != null){
            if(cur.val != val){
                stack.push(cur);
            }
            cur = cur.next;
        }
        while(!stack.isEmpty()){
            stack.peek().next = cur;
            cur = stack.pop();
        }
        return cur;
    }
}

【代碼2】

時間複雜度O(n)，空間複雜度O(1)

class Solution {
    public ListNode deleteNode(ListNode head, int val) {
        while(head != null){
            if(head.val != val){
                break;
            }
            head = head.next;
        }
        ListNode cur = head;
        ListNode pre = head;
        while(cur != null){
            if(cur.val == val){
                pre.next = cur.next;
            }else{
                pre = cur;
            }
            cur = cur.next;
        }
        return head;
    }
}