leetcode 1171 Remove Zero Sum Consecutive Nodes from Linked List

1. 每一轮，如果有可以删除的（和为0），则删除，并从头开始遍历；如果没有可以删除的，则右移left。

class Solution {
public:
    ListNode* removeZeroSumSublists(ListNode* head) {
        head=reverseList(head);
        ListNode ln(0);ln.next=head;
        ListNode *left=head,*lpre=&ln,*right=head;
        while(left) {
            right=left;
            int sum=0;
            while(right) {
                sum+=right->val;
                if(sum==0) {
                    lpre->next=right->next;
                    /*while(left!=lpre->next) {
                        ListNode* tmp=left->next;
                        delete left;
                        left=tmp;
                    }*/ 不能释放这些空间，如果释放，不能通过测试用例[0],报heap-use-after-free错误。
                    break;
                }
                else {
                    right=right->next;
                }
            }//while
            if(right) {lpre=&ln;left=ln.next;}
            else {lpre=left;left=left->next;}
        }//while
       head=reverseList(ln.next);
        return head;
    }
    ListNode* reverseList(ListNode* head) {
        ListNode *pre=nullptr,*cur=head,*next=head;
        while(cur) {
            next=cur->next;
            cur->next=pre;
            pre=cur;
            cur=next;
        }
        return pre;
    }
};

2. https://leetcode.com/problems/remove-zero-sum-consecutive-nodes-from-linked-list/discuss/549912/C%2B%2B-8ms

删除之后，继续遍历时，删除的情况比如：-3 3 -2 2

class Solution {
public:
    ListNode* removeZeroSumSublists(ListNode* head) {
        ListNode ln(0);ln.next=head;
        ListNode* pre=&ln,*right=head;
        int sum=0;
        while(right) {
            sum+=right->val;
            if(sum==0) pre->next=right->next;
            right=right->next;
            if(!right) {
                pre=pre->next;
                if(!pre) break;
                right=pre->next;
                sum=0;
            }
        }
        return ln.next;
    }
};

3. 递归

class Solution {
public:
    ListNode* removeZeroSumSublists(ListNode* head) {
        if(!head) return head;
        ListNode* ans=removeZeroSumSublists(head->next);
        head->next=ans;
        int sum=head->val;
        if(sum==0) {
            head->next=nullptr;
            return ans;
        }
        ListNode* node=head->next;
        while(node) {
            sum+=node->val;
            if(sum==0) {
                return node->next;
            }
            node=node->next;
        }
        return head;
    }
};