C/C++查找

对于未排好序的数，用顺序查找；
已排好序的数，用顺序查找或折半查找都可，折半查找效率更高。

两种查找算法的动画演示：

顺序查找：

#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;
}

折半查找（二分查找）：

• 迭代/循环实现

#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;
}

• 递归实现

#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;
}