LeetCode OJ

题目：

　　Sort a linked list using insertion sort.

解题思路：

　　假设 list[1..i]是排好序的，找到第i+1个元素应该插入的位置及其前驱，然后将其插入。

代码：

　　

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *insertionSortList(ListNode *head) {
        if (head == NULL || head->next == NULL) {
            return head;
        }
        
        /*找到最小的元素作为表头*/
        ListNode *p_tmp = head;
        int min_val = head->val;
        
        ListNode *p_current = head->next;
        while (p_current != NULL) {
            if (p_current->val < min_val) {
                p_tmp = p_current;
                min_val = p_current->val;
            }
            p_current = p_current->next;
        }
        p_tmp->val = head->val;
        head->val = min_val;
        
        ////////////////////////////////////////////////////////
        p_current = head->next;
        while (p_current != NULL){
            ListNode *p_next = p_current->next;

            ListNode *p_pos = head; //找插入位置
            while (p_pos != p_current && p_pos->next->val <= p_current->val) p_pos = p_pos->next;

            ListNode *p_pre = head;  // 找前驱
            while (p_pre->next != p_current) p_pre = p_pre->next;

            if (p_pos != p_current) {
                p_pre->next = p_current->next;
                p_current->next = p_pos->next;
                p_pos->next = p_current;
            }

            p_current = p_next;
        }
        return head;
    }
};