For unsorted numbers, use sequential search;
for sorted numbers, use sequential search or half search, which is more efficient.
Animated demonstration of two search algorithms:
sequential search:
#include <iostream>
using namespace std;
int SequenceSearch(int *a, int len, int num)
{
int i;
for(i=0; i<len; i++)
{
if(a[i]==num)
{
return i;
}
}
return -1;
}
int main()
{
int a[]={
1,3,5,7,9,0,2,4,6,8};
int len = sizeof(a)/sizeof(a[0]);
int result = SequenceSearch(a,len,3);
if(result >= 0)
cout << "数字" << a[result] << "的数组下标为" << result << endl;
else
cout << "没找到" << endl;
return 0;
}
Binary search (binary search) :
- Iterative/loop implementation
#include <iostream>
using namespace std;
int BinarySearch(int *a, int len, int num)
{
int low=0, high=len-1, mid;
while(low<=high)
{
mid=(low+high)/2;
if(num==a[mid])
return mid;
else if(num<a[mid])
high=mid-1;
else
low=mid+1;
}
return -1;
}
int main()
{
int a[]={
1,3,5,7,9,0,2,4,6,8};
int len = sizeof(a)/sizeof(a[0]);
int result = BinarySearch(a,len,7);
if(result >= 0)
cout << "数字" << a[result] << "的数组下标为" << result << endl;
else
cout << "没找到" << endl;
return 0;
}
- Recursive implementation
#include <iostream>
using namespace std;
int BinarySearch(int *a, int num, int low, int high)
{
int mid;
if(low<=high)
{
mid=(low+high)/2;
if(num==a[mid])
return mid;
else if(num<a[mid])
return BinarySearch(a, num, low, mid-1);
else
return BinarySearch(a, num, mid+1, high);
}
return -1;
}
int main()
{
int a[]={
1,3,5,7,9,0,2,4,6,8};
int len = sizeof(a)/sizeof(a[0]);
int result = BinarySearch(a,7,0,len-1);
if(result >= 0)
cout << "数字" << a[result] << "的数组下标为" << result << endl;
else
cout << "没找到" << endl;
return 0;
}