初识 二分查找

O(log n), 也叫对数时间，这样的算法包括二分查找

O(n) , 也叫线性时间，这样的算法包括简单查找

O(n*log n),快速排序——一种较快的排序算法

O(n^2), 选择排序——一种较慢的排序算法

O(n!), 旅行商问题解决方案—一种非常慢的算法

二分查找测试

#include
#include
#include
#define NUM 5
int binary(int* list, int item);
int main() {
	int find,find1;
	int num[NUM] = { 1,3,5,7,9 };
	find = binary(num, 3);
	find1 = binary(num, -1);
	printf("%dn%d", find, find1);
}
int binary(int *list,int item){
	int mid;
	int guess;
	int low = 0;
	int high = NUM- 1;
	while (low <= high){
		mid = (low + high) / 2;
	guess = list[mid];
	if (guess == item)
		return list[mid];
	if (guess > item)
		high = mid - 1;
	if (guess < item)
		low = mid + 1;
	}
	return NULL;

}

用二分查找在有序列表中查找人名

#include
#include
#include
#define NUM 5
int binary(const char* list[], const char* item);
int main() {
	int find_qsort,find1_qsort;
	const char* list[10] = {
	"Amelia",
	"Ava",
	"Charlotte",
	"Emma",
	"Mia",
	"Isabella",
	"Olivia",
	"Sophia",
	"Zala"
	};
	find_qsort = binary(list, "Ava");
	find1_qsort = binary(list, "Mia");
	printf("%sn%s", list[find_qsort], list[find1_qsort]);
}
int binary(const char *list[],const char *item){
	int mid;
	const char* guess;
	int low = 0;
	int high = NUM- 1;
	while (low <= high){
		mid = (low + high) / 2;
	guess = list[mid];
	if (guess == item)
		return mid;
	if (guess > item)
		high = mid - 1;
	if (guess < item)
		low = mid + 1;
	}
	return NULL;

}