排序数组中的递归二进制搜索C ++

Question

I have to write a recursive function which searches through a sorted array.

#include <iostream>
using namespace std;

int find(int value, int* folge, int max) {

}


int main() {
    int const n = 7;
    int wert1 = 4, wert2 = 13, wert3 = 2, wert4 = 25;
    int folge[n] = {3,4,9,13,13,17,22};
    wert1 = find(wert1, folge, n);
}

This is the part of code that was given to us and we have to finish it.
I know how to do this if you have 4 variables available. (min and max) But I only have three, is there a way to edit the start point of the array which is given to the next function?

Answer 1

Suppose you have your four-param version:

find(value, array, min, max);

with the three-parameter version you can call:

find(value, array + min, max);

Note that the max 'th element of array is actually max-min th element of array + min , so depending on your implementation you may want to call

find(value, array + min, max - min);

Answer 2

The function can be written the following way

#include <iostream>

int find( int value, int* folge, int max ) 
{
    if ( max == 0 ) return -1;

    int middle = max / 2;

    if ( folge[middle] == value ) return middle;

    bool lower = value < folge[middle];
    int n = lower ? find( value, folge, middle ) 
                  : find( value, folge + middle + 1, max - middle - 1 );

    return n != -1 && !lower ? n + middle + 1: n; 
}

int main()
{
    int const n = 7;
    int wert1 = 4, wert2 = 13, wert3 = 2, wert4 = 25;
    int folge[n] = {3,4,9,13,13,17,22};

    std::cout << wert1 << " = " << find(wert1, folge, n) << std::endl;
    std::cout << wert2 << " = " << find(wert2, folge, n) << std::endl;
    std::cout << wert3 << " = " << find(wert3, folge, n) << std::endl;
    std::cout << wert4 << " = " << find(wert4, folge, n) << std::endl;

    return 0;
}

The program output is

4 = 1
13 = 3
2 = -1
25 = -1

Or one more test program

#include <iostream>

int find( int value, int* folge, int max ) 
{
    if ( max == 0 ) return -1;

    int middle = max / 2;

    if ( folge[middle] == value ) return middle;

    bool lower = value < folge[middle];
    int n = lower ? find( value, folge, middle ) 
                                  : find( value, folge + middle + 1, max - middle - 1 );

    return n != -1 && !lower ? n + middle + 1: n; 
}

int main()
{
    int const n = 7;
    int folge[n] = {3,4,9,13,13,17,22};

    for ( int x : { 2, 3, 4, 9, 13, 17, 22, 25 } )
    {
        std::cout << x << " -> " << find( x , folge, n ) << std::endl;  
    }        

    return 0;
}

Its output is

2 -> -1
3 -> 0
4 -> 1
9 -> 2
13 -> 3
17 -> 5
22 -> 6
25 -> -1

Answer 3

find( &folge[1],...) // ignore first element

第n个元素的地址是一个大小为Size-n的数组

Answer 4

You can change the value of the int pointer folge

int find(int value, int* folge, int max) {
   if (max == 0) {
        return -1;
   }

   int mid=max/2;

   if (value == folge[mid])
   {
        return mid;
   }

   int base=0;

   if (value < folge[mid])
   {
       max=mid-1;
   }
   else
   {
       max-=(mid+1);
       base=mid+1;
   }

   int ret=find(value,folge+base,max);

   if (ret == -1)
   {
       return -1;
   }

   return ret+base;
}

Answer 5

If folge points to the first element, then folge+1 will point to the second.

int find(int value, int* folge, int max)
{
    int m = max/2;
    if (0 == max)
    {
        return -1;
    }

    if (value == folge[m])
    {
        return value;
    }
    else if (value < folge[m])
    {
        return find(value, folge, m);
    } else
    {
        return find(value, folge + m + 1, max - m - 1);
    }
}