Reverse nodes in K group

Signed-off-by: begeekmyfriend <[email protected]>

025_reverse_nodes_in_k_group/Makefile

@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test reverse_nodes.c

025_reverse_nodes_in_k_group/reverse_nodes.c

@@ -0,0 +1,77 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+struct ListNode {
+    int val;
+    struct ListNode *next;
+};
+
+static struct ListNode* reverseKGroup(struct ListNode* head, int k) {
+    if (head == NULL || k <= 1) {
+        return head;
+    }
+
+    int first = 1;
+    struct ListNode dummy;
+    dummy.next = head;
+    struct ListNode *dhead = &dummy;
+    struct ListNode *prev = head;
+    struct ListNode *p = head->next;
+    struct ListNode *next = p == NULL ? NULL : p->next;
+    while (p != NULL) {
+        int i;
+        struct ListNode *end = dhead->next;
+        for (i = 0; end != NULL && i < k; i++) {
+            end = end->next;
+        }
+        if (i < k) {
+            break;
+        }
+
+        while (p != end) {
+            p->next = dhead->next;
+            dhead->next = p;
+            prev->next = next;
+            p = next;
+            next = p == NULL ? NULL : p->next;
+        }
+
+        if (first) {
+            first = 0;
+            dummy.next = dhead->next;
+        }
+
+        dhead = prev;
+        prev = p;
+        p = p == NULL ? NULL : p->next;
+        next = p == NULL ? NULL : p->next;
+    }
+    return dummy.next;
+}
+
+int main(int argc, char **argv)
+{
+    int i;
+    struct ListNode *p, *prev, dummy, *list;
+
+    dummy.next = NULL;
+    prev = &dummy;
+    for (i = 2; i < argc; i++) {
+        p = malloc(sizeof(*p));
+        int n = atoi(argv[i]);
+        printf("%d ", n);
+        p->val = n;
+        p->next = NULL;
+        prev->next = p;
+        prev = p;
+    }
+    putchar('\n');
+
+    list = reverseKGroup(dummy.next, atoi(argv[1]));
+    for (p = list; p != NULL; p = p->next) {
+        printf("%d ", p->val);
+    }
+    putchar('\n');
+
+    return 0;
+}