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  • [leetcode]Sort List

    merge sort,记了长度。如果断开链表时把第一个链表的最后一个节点的next设为NULL,就不用在函数参数里传长度了。一直错误是因为在生成的链表最后的next没有设成NULL。用了dummy node很有用。

    可以借鉴http://blog.csdn.net/sunbaigui/article/details/16843419 最后直接把剩余的链表接过来。

    class Solution {
    public:
        ListNode *sortList(ListNode *head) {
            int size = 0;
            ListNode *node = head;
            while (node != NULL) {
                node = node->next;
                size++;
            }
            return mergeSort(head, size);
        }
        
        ListNode* mergeSort(ListNode *node, int size) {
            if (size == 0 || size == 1)
                return node;
            int half = size / 2;
            ListNode* head1 = node;
            ListNode* head2 = node;
            for (int i = 0; i < half; i++) {
                head2 = head2->next;
            }
            head1 = mergeSort(head1, half);
            head2 = mergeSort(head2, size - half);
    
            ListNode *dummy = new ListNode(0);
            ListNode *prev = dummy;
            ListNode *n1 = head1;
            ListNode *n2 = head2;
            int n1Step = 0;
            int n2Step = 0;
            while (n1Step != half && n2Step != size - half) {
                if (n1->val <= n2->val) {
                    prev->next = n1;
                    n1 = n1->next;
                    n1Step++;
                }
                else {
                    prev->next = n2;
                    n2 = n2->next;
                    n2Step++;
                }
                prev = prev->next;
            }
            while (n2Step != size - half) {
                prev->next = n2;
                prev = prev->next;
                n2 = n2->next;
                n2Step++;
            }
            while (n1Step != half) {
                prev->next = n1;
                prev = prev->next;
                n1 = n1->next;
                n1Step++;
            }
            prev->next = NULL;
            return dummy->next;
        }
    };
    

      

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  • 原文地址:https://www.cnblogs.com/lautsie/p/3521694.html
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