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Reverse a link-list without any additional pointer?

+3 votes
4,388 views

Is it possible if yes can someone share the code in C?

posted Dec 2, 2013 by anonymous

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1 Answer

0 votes

If recursion is okay, then u need to walk the list recursively, and then reverse the list as you unwind. This can be accomplished by allowing another parameter to the recursive call to provide the pointer needed to walk through the beginning the list as the recursive calls are unwinding from the end. This implementation uses no extra local variables per recursive call, only the variables provided in the parameters.

void swap_left (node *a, node *b, int tmp) {
    a->data = b->data;
    b->data = tmp;
}

void reverse_recursively (node *cur, node **tail) {
    if (cur) {
        reverse_recursively(cur->next, tail);
        if (*tail) {
            swap_left(cur, *tail, cur->data);
            if (cur != *tail) *tail = (*tail)->next;
            if (cur == *tail) *tail = 0;
        }
    }
}

void reverse (node *list) {
    reverse_recursively(list, &list);
}
answer Dec 11, 2013 by Naveena Garg
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List => 1 --->  2 --->  3 --->  4 ---> 5 ---> 6
                                      /        \
                                    10          7
                                     \          /
                                      9 <---  8


OURTPUT => 1 --->  2 --->  3 --->  4 ---> 10 ---> 9
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                                        5           8
                                         \          /
                                          6 <---  7
...