C++顺序表折半查找

算法思想

折半查找：又称二分查找，适用于有序的顺序表。
   先将中间位置元素与Key进行比较
      若相等，则返回中间位置下标
      若不相等：
       ① key<中间值，在左半边继续查找
       ② key>中间值，在右半边继续查找

算法实现

int BinarySearch(sqList L,int key)
{
	int low=0,high=L.length-1;
	while(low<=high)//'<='很关键
	{
		int mid=(low+high)/2;
		if(L.data[mid]==key)
			return mid+1;
		else if(key<L.data[mid])
			high=mid-1;
		else
			low=mid+1;
	}
	return  -1;
}

运行代码

#include "stdafx.h"
#include<iostream>
using namespace std;
#define MaxSize 50

typedef struct
{
	int data[MaxSize];
	int length;
}sqList;
void Creat(sqList &L);
int Search(sqList L,int key);//顺序查找
int Binary_Search(sqList L,int key);//二分查找
int _tmain(int argc, _TCHAR* argv[])
{
	sqList l;int x;
	Creat(l);
	cout<<"2在第"<<Binary_Search(l,2)<<"个位置。"<<endl;
	cout<<"5在第"<<Binary_Search(l,5)<<"个位置。"<<endl;
	system("pause");
	return 0;
}
void Creat(sqList &L)
{ 
	for(int i=0;i<5;i++)
	{
		L.data[i]=i+1;
	}
	L.length =5;
	for (int i = 0; i < L.length; i++)
	{
		cout<<L.data[i]<<" ";
	}
	cout<<endl<<endl;
}
int Search(sqList L,int key)
{
	for (int i = 0; i < L.length; i++)
	{
		if(L.data[i]==key)
			return i+1;
	}
	return -1;
}
int Binary_Search(sqList L,int key)
{
	int low=0,high=L.length-1;
	while(low<=high)//‘<=’很关键
	{
		int mid=(low+high)/2;
		if(L.data[mid]==key)
			return mid+1;
		else if(key<L.data[mid])
			high=mid-1;
		else
		    low=mid+1;
	}
	return -1;
}

运行结果

来源：CSDN

作者：Demon、

链接：https://blog.csdn.net/weixin_43656327/article/details/104755545