本文主要總結二分查找算法的遞歸實現與非遞歸實現,二分查找算法的時間複雜度爲,且只能針對已經排好序的數組進行查找。
1.非遞歸的實現:
1.1 首先設置3個索引,分別指向開始,結束和中間位置,即start=0,end=len-1,mid=(start+end)/2;start向右移動,end向左移動,當start>end則跳出循環,即在while(start<=end)中進行循環.
1.2 在循環中首先比較find與arr[mid],若find==arr[mid],則直接return mid;若find>arr[mid],則start = mid + 1;進行下次循環。若find<arr[mid],則end= mid - 1;進行下次循環。否則返回-1;
代碼如下:
//非遞歸進行二分查找
int Binary_Search_No_Recursion(int * arr, int len, int find_data)
{
int start = 0, end = len - 1;
while (start<=end)
{
int mid = (start + end) / 2;
if (arr[mid]==find_data)
{
return mid;
}
else if (arr[mid] < find_data)
{
start = mid + 1;
}
else
{
end = mid - 1;
}
}
return -1;
}
2.遞歸實現:
2.1 原理同上,首先取出mid位置,在if中進行判斷,若arr[mid]<find_data,表示待尋找的數據在中間的右邊,需要改變start爲mid+1,則遞歸執行Binary_Search_Recursion(arr, find_data, mid + 1, end);
2.2 若arr[mid]>find_data,表示待尋找的數據在中間的左邊,需要改變end爲mid-1,則遞歸執行Binary_Search_Recursion(arr, find_data, start, mid-1);
2.3 若arr[mid]==find_data,則直接返回mid。
代碼如下:
//遞歸進行二分查找
int Binary_Search_Recursion(int * arr, int find_data,int start, int end)
{
int mid = (start + end) / 2;
if (start>end)
{
return -1;
}
else if(arr[mid]<find_data)
{
return Binary_Search_Recursion(arr, find_data, mid + 1, end);
}
else if (arr[mid] > find_data)
{
return Binary_Search_Recursion(arr, find_data, start, mid-1);
}
else if (arr[mid] == find_data)
{
return mid;
}
}
總體實現:
#include "pch.h"
#include <iostream>
using namespace std;
//非遞歸進行二分查找
int Binary_Search_No_Recursion(int * arr, int len, int find_data)
{
int start = 0, end = len - 1;
while (start<=end)
{
int mid = (start + end) / 2;
if (arr[mid]==find_data)
{
return mid;
}
else if (arr[mid] < find_data)
{
start = mid + 1;
}
else
{
end = mid - 1;
}
}
return -1;
}
//遞歸進行二分查找
int Binary_Search_Recursion(int * arr, int find_data,int start, int end)
{
int mid = (start + end) / 2;
if (start>end)
{
return -1;
}
else if(arr[mid]<find_data)
{
return Binary_Search_Recursion(arr, find_data, mid + 1, end);
}
else if (arr[mid] > find_data)
{
return Binary_Search_Recursion(arr, find_data, start, mid-1);
}
else if (arr[mid] == find_data)
{
return mid;
}
}
int main()
{
int arr[] = { 1,2,3,4,5,6,7,8,9,10 };
int len = sizeof(arr) / sizeof(int);
int find = 10;
cout << Binary_Search_No_Recursion(arr,len,find) << endl;
cout << Binary_Search_Recursion(arr, find,0,len-1) << endl;
}