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| 1 | +#include <stdio.h> |
| 2 | +#include <stdlib.h> |
| 3 | +#include <stdbool.h> |
| 4 | + |
| 5 | +struct ListNode { |
| 6 | + int val; |
| 7 | + struct ListNode *next; |
| 8 | +}; |
| 9 | + |
| 10 | +struct ListNode* createNode(int data) { |
| 11 | + struct ListNode *new_node = (struct ListNode *)malloc(sizeof(struct ListNode)); |
| 12 | + new_node->val = data; |
| 13 | + new_node->next = NULL; |
| 14 | + return new_node; |
| 15 | +} |
| 16 | + |
| 17 | +struct ListNode* reverseKGroup(struct ListNode* head, int k) { |
| 18 | + if (k <= 1 || head == NULL) return head; |
| 19 | + |
| 20 | + struct ListNode *leap = head, *next_leap = NULL; |
| 21 | + struct ListNode *milestone = NULL, *next_milestone = NULL; |
| 22 | + struct ListNode *new_head = NULL; |
| 23 | + bool first = true; |
| 24 | + int len = 0; |
| 25 | + while (leap) { |
| 26 | + leap = leap->next; |
| 27 | + len++; |
| 28 | + } |
| 29 | + |
| 30 | + if (k > len) return head; |
| 31 | + |
| 32 | + leap = head; |
| 33 | + while (leap) { |
| 34 | + int step = k - 1; |
| 35 | + milestone = leap; |
| 36 | + while (milestone && step) { |
| 37 | + milestone = milestone->next; |
| 38 | + step--; |
| 39 | + } |
| 40 | + |
| 41 | + if (milestone == NULL) { |
| 42 | + break; |
| 43 | + } |
| 44 | + |
| 45 | + step = k - 1; |
| 46 | + next_milestone = milestone->next; |
| 47 | + while (next_milestone && step) { |
| 48 | + next_milestone = next_milestone->next; |
| 49 | + step--; |
| 50 | + } |
| 51 | + |
| 52 | + if (next_milestone == NULL) { |
| 53 | + next_milestone = (milestone == NULL) ? NULL : milestone->next; |
| 54 | + } |
| 55 | + |
| 56 | + next_leap = milestone->next; |
| 57 | + milestone->next = NULL; |
| 58 | + |
| 59 | + /* reverse group */ |
| 60 | + struct ListNode *p = leap, *q = NULL, *t = NULL; |
| 61 | + while (p) { |
| 62 | + t = p->next; |
| 63 | + p->next = q; |
| 64 | + q = p; |
| 65 | + p = t; |
| 66 | + } |
| 67 | + leap->next = next_milestone; /* group tail to next milestone */ |
| 68 | + |
| 69 | + if (first) { |
| 70 | + new_head = milestone; |
| 71 | + first = false; |
| 72 | + } |
| 73 | + |
| 74 | + leap = next_leap; |
| 75 | + } |
| 76 | + |
| 77 | + return new_head; |
| 78 | +} |
| 79 | + |
| 80 | +int main() { |
| 81 | + int n = 5; |
| 82 | + int k = 3; |
| 83 | + |
| 84 | + struct ListNode *head = createNode(1); |
| 85 | + struct ListNode *p = head; |
| 86 | + |
| 87 | + int i; |
| 88 | + for (i = 2; i <= n; i++) { |
| 89 | + p->next = createNode(i); |
| 90 | + p = p->next; |
| 91 | + } |
| 92 | + |
| 93 | + p = head; |
| 94 | + while (p) { |
| 95 | + printf("%d->", p->val); |
| 96 | + p = p->next; |
| 97 | + } |
| 98 | + printf("NIL\n"); |
| 99 | + |
| 100 | + struct ListNode *new_head = reverseKGroup(head, k); |
| 101 | + |
| 102 | + p = new_head; |
| 103 | + while (p) { |
| 104 | + printf("%d->", p->val); |
| 105 | + p = p->next; |
| 106 | + } |
| 107 | + printf("NIL\n"); |
| 108 | + |
| 109 | + return 0; |
| 110 | +} |
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