147. Insertion Sort List [LeetCode]

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147. Insertion Sort List

链表排序，插入排序

class Solution {

public:

    ListNode * insertionSortList(ListNode * head) {

         if (head == nullptr || head-> next == nullptr) return head;

         //创建一个系统最小节点

        ListNode dummy(INT_MIN);

         for (ListNode *cur = head; cur;) {

             auto pos = findInsertPos( &dummy, cur-> val);

             //把cur节点插入pos节点之后

            ListNode *tmp = cur-> next;

            cur-> next = pos-> next;

            pos-> next = cur;

            cur = tmp;

        }

         return dummy. next;

    }

    ListNode * findInsertPos(ListNode *head, int x) {

        ListNode *pre = nullptr;

         for (ListNode *cur = head; cur &&cur-> val <= x; pre = cur, cur = cur-> next);

         return pre;

    }

};