简单的算法

x = (x & 0x55) << 1 | (x & 0xAA) >> 1;

x = (x & 0x33) << 2 | (x & 0xCC) >> 2;

x = x <<4 | x>>4;

/*
此算法实现将一个整数拆成一串连续的整数之和。如：6可以拆分成：1+2+3.
    微调的思想，不用等差列表求和的思想。
    2011-9-24.
   */
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int
main(int argc, char * argv[])
{
    int n = atoi(argv[1]);
    int left, right;
    int sum ;
    int count = 0;

    printf("n = %d\n",n );
    if (n <= 0) return;

    sum = 1;
    for (right = left = 1; right <= (n + 1) /2; ) {
        if (sum > n) {
            sum -= left;
            left++;
        } else if (sum == n) {
            printf("start pos = %d, end pos = %d, total num = %d\n",
                left, right, right - left + 1);
            count++;
            sum -= left;
            left++;
        } else {
            right++;
            sum += right;
        }
    }
    printf("have %d!\n", count);
}

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

struct test_t {
	struct test_t *next;
	int a;
};
int
create_list(struct test_t **head, int *arr, int num)
{
	int i;
	struct test_t *walker;

	for (i = 0; i < num; i++) {
		walker = (struct test_t *)malloc(sizeof(*walker));
		walker->a = arr[i];
		walker->next = *head;
		*head = walker;
	}

	return 0;
}

void
print_list(struct test_t *head)
{
	struct test_t *walker;

	for (walker = head; walker; walker = walker->next) {
		printf(" %d", walker->a);
	}
	printf("\n");
}

int
sort_list(struct test_t **head)
{
	struct test_t *walker, *swap, *tail, *prev;
	int count = 1;
//	print_list(*head);
	tail = NULL;
	while (*head != tail) {
		for (walker = *head; walker->next != tail;) {
			if (walker->a > walker->next->a) {
				if (walker == *head) {
					*head = walker->next;
				} else {
					prev->next = walker->next;
				}
				prev = walker->next;
				walker->next = walker->next->next;
				prev->next = walker;
			} else {
				prev = walker;
				walker = walker->next;
			}
		}
		printf("%d:\n", count);
		print_list(*head);
		count++;
		tail = walker;
	}
}

int
main(void)
{
	int arr[] = {1,3,27,6,3,20,68,15,35};
	int num;
	struct test_t *head = NULL;
	
	num = sizeof(arr) / sizeof(int); 

	create_list(&head, arr, num);
	print_list(head);

	sort_list(&head);
	print_list(head);
}