Created
April 19, 2010 22:30
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/* | |
Binary search on a queue. Complexity approaches 2*N (I think). | |
Worse than linear search. I feel dirty now. | |
*/ | |
#include <stdio.h> | |
#include <stdlib.h> | |
struct item { | |
struct item *next; | |
int mark; | |
int x; | |
}; | |
struct item * | |
make_list (int i, int x, int y) | |
{ | |
struct item *it = malloc(sizeof(struct item)); | |
it->mark = 0; | |
if (0 == i) { | |
it->next = NULL; | |
it->x = x + y; | |
} else { | |
it->next = make_list(i - 1, y, x + y); | |
it->x = x + y; | |
} | |
return it; | |
} | |
void | |
print_list (struct item *it) | |
{ | |
printf("%07d%c", it->x, it->mark ? '!' : ' '); | |
if (NULL != it->next) { | |
print_list(it->next); | |
} | |
} | |
/* Use of goto instead of recursion, just to make it extra painful. */ | |
void | |
search_list (const int g, struct item *start) | |
{ | |
struct item *lo = start, *hi, *slow = start, *fast = start; | |
int ab = 1; | |
while (NULL != fast->next) { | |
fast = fast->next; | |
if (ab ^= 1) { | |
slow = slow->next; | |
} | |
} | |
if (slow->x >= g) { | |
lo = start; | |
hi = slow; | |
} else { | |
lo = slow; | |
hi = fast; | |
} | |
down: | |
if (slow->next == fast) { | |
goto end; | |
} | |
ab = 1; | |
slow = fast = lo; | |
while (hi != fast) { | |
fast = fast->next; | |
if (ab ^= 1) { | |
slow = slow->next; | |
} | |
} | |
if (slow->x >= g) { | |
hi = slow; | |
} else { | |
lo = slow; | |
hi = fast; | |
} | |
goto down; | |
end: | |
if (slow->x == g) { | |
slow->mark = 1; | |
} | |
if (fast->x == g) { | |
fast->mark = 1; | |
} | |
} | |
int | |
main (void) | |
{ | |
struct item *it = make_list(29, 0, 1); | |
print_list(it); | |
printf("\nsearch for 610 ...\n"); | |
search_list(610, it); | |
print_list(it); | |
return EXIT_SUCCESS; | |
} |
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