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在一个有序数组中通过二分查找法来找出具体某个数字

Gascognya 2022-03-25 阅读 30
c语言

1.直接用二分法查找

#include<stdio.h>
int main()
{
	int arr[] = { 1,2,3,4,5,6,7,8,9,10 };//建立一个有序的数组
	int k;
	scanf("%d", &k);//输入你要查找的数
	int left = 0;
	int sz = sizeof(arr) / sizeof(arr[0]);//计算数组的长度
	int right = sz - 1;
	while (left <= right)
	{
		int mid = (left + right) / 2;
		if (arr[mid] > k)
		{
			right = mid - 1;
		}
		else if (arr[mid] < k)
		{
			left = mid + 1;
		}
		else
		{
			printf("找到了,下标是%d", mid);
			break;
		}
	}
	if (left > right)
		printf("找不到了\n");
	return 0;
}

2.写一个函数来表达二分查找法

#include<stdio.h>
int binary_search(int arr[], int k, int sz)
{
	int left = 0;
	int right = sz - 1;
	while (left <= right)
	{
		int mid = (left + right) / 2;
		if (arr[mid] > k)
		{
			right = mid - 1;
		}
		else if (arr[mid] < k)
			left = mid + 1;
		else
		{
			return mid;
		}
	}
	return -1;
}
int main()
{
	int arr[] = { 1,2,3,4,5,6,7,8,9,10 };
	int k;
	scanf("%d", &k);
	int sz = sizeof(arr) / sizeof(arr[0]);
	int ret=binary_search(arr, k, sz);
	if (ret == -1)
		printf("没找到\n");
	else
		printf("找到了,下标是%d\n", ret);
	return 0;
}
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