【LeetCode】92. Reverse Linked List II
2014-12-04 16:59
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Reverse Linked List II
Reverse a linked list from position m to n. Do it in-place and in one-pass.
For example:
Given
return
Note:
Given m, n satisfy the following condition:
1 ≤ m ≤ n ≤ length of list.
把[m,n]那一段抠出来,reverse之后,再拼回去。
需要注意的是,reverse函数的参数需要是指针引用*&。
附:指针传递与指针引用传递的区别
Reverse a linked list from position m to n. Do it in-place and in one-pass.
For example:
Given
1->2->3->4->5->NULL, m = 2 and n = 4,
return
1->4->3->2->5->NULL.
Note:
Given m, n satisfy the following condition:
1 ≤ m ≤ n ≤ length of list.
把[m,n]那一段抠出来,reverse之后,再拼回去。
需要注意的是,reverse函数的参数需要是指针引用*&。
附:指针传递与指针引用传递的区别
当我们把指针做为参数传递时,其实是把指针的副本传递给了函数,也可以说传递指针是指针的值传递。这样当我们在函数内部修改指针时,在函数里修改只是修改的指针的副本,而不是指针本身,原来的指针还保留着原来的值。
/** * Definition for singly-linked list. * struct ListNode { * int val; * ListNode *next; * ListNode(int x) : val(x), next(NULL) {} * }; */ class Solution { public: ListNode *reverseBetween(ListNode *head, int m, int n) { if(head == NULL) return head; ListNode *newhead = new ListNode(-1); newhead->next = head; ListNode *prebegin = newhead; ListNode *begin = head; ListNode *end = newhead; ListNode *postend = head; while(--m) { prebegin = prebegin->next; begin = begin->next; } while(n--) { end = end->next; postend = postend->next; } //reverse reverse(begin, end); //link prebegin->next = begin; end->next = postend; return newhead->next; } void reverse(ListNode*& begin, ListNode*& end) { if(begin == end) return; else if(begin->next == end) end->next = begin; else {//at least 3 nodes ListNode* pre = begin; ListNode* cur = pre->next; ListNode* post = cur->next; while(post != end->next) { cur->next = pre; pre = cur; cur = post; post = post->next; } cur->next = pre; } //swap ListNode* temp = begin; begin = end; end = temp; } };
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