71 lines
1.8 KiB
C++
71 lines
1.8 KiB
C++
#include <stack>
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class Solution {
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public:
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ListNode * reverseKGroup(ListNode* head, int k) {
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ListNode* seg_start = head;
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ListNode* now = head;
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ListNode* return_head = head;
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ListNode* last_seg = NULL;
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int passed = 0;
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while (now != NULL)
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{
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passed++;
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if (passed == k)
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{
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// Meet a segment
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ListNode* seg_end = now;
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// Change head
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if (seg_start == head)
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{
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return_head = seg_end;
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}
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ListNode* p = seg_start;
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std::stack<ListNode*> stk;
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while (p != seg_end)
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{
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stk.push(p);
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p = p->next;
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}
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// p is now seg_end
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// checkpoint
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ListNode* next_seg_start = seg_end->next;
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while (!stk.empty())
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{
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p->next = stk.top();
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stk.pop();
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p = p->next;
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}
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// stack is empty. p is now seg_start.
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// p->next now pointes to the orignal "next"
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// set last segment
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if (last_seg)
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{
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last_seg->next = seg_end;
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}
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last_seg = seg_start;
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// set it to next_seg_start
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p->next = next_seg_start;
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seg_start = next_seg_start;
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now = next_seg_start;
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passed = 0;
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// debug
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//printList(return_head);
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}
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else
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{
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now = now->next;
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}
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}
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return return_head;
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}
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};
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