线性表顺序存储-练习题3-逆置顺序表

题目：

        以顺序表做存储结构实现线性表，实现就地逆置算法，即在原表的存储空间将线性表(a1, a2, ..., an)逆置为(an, ... , a2, a1).

思路：

1. 须要考虑的线性表个数的奇/偶数状况，奇/偶数状况不一样，置换的步伐长度不一样
2. 设置一个中转数，当作数置换时作中转存储

代码：

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

#define MAXSIZE 101

typedef struct {
	int r[MAXSIZE];
	int length;
} SqList;

void inverseElement(SqList *L);
void print(SqList L);
int main(int argc, char *argv[]) {
	SqList list;
	int i;
	list.length = 9;
	for (i = 1; i <= list.length; i++) {
		list.r[i] = i * 3;
	}
	printf("初始顺序表：\n");
	print(list);
	printf("\n");
	inverseElement(&list);
	printf("置换后的顺序表：\n");
	print(list);
	return 0;
}

/**
 *  逆置顺序表
 */
void inverseElement(SqList *L) {
	int middle = 0, k = -1, i;
	if (L->length % 2 == 0) {
		for (i = L->length / 2; i > 0; i--) {
			k += 2;
			middle = L->r[i];
			L->r[i] = L->r[i + k];
			L->r[i + k] = middle;
		}
	} else {
		k = 0;
		for (i = L->length / 2; i > 0; i--) {
			k += 2;
			middle = L->r[i];
			L->r[i] = L->r[i + k];
			L->r[i + k] = middle;
		}
	}
}

void print(SqList L) {
	for (int i = 1; i <= L.length; i++) {
		printf("%d\t", L.r[i]);
	}
}