二分查找

#include <iostream>
using namespace std;
//普通二分法
int BinarySearch_I(int* a, int n, int x);
//递归二分法
int BinarySearch_R(int* a,int x,int left,int right);
//普通二分法测试
void test01();
//递归二分法测试
void test02();

int main()
{
    //test01();
    test02();
    return 0;
}
int BinarySearch_I(int* a, int n, int x)
{
    int left = 0, right = n;
    while (left < right)
    {
        int mid = (right + left) / 2;
        if (a[mid] > x) right = mid - 1;
        else if (a[mid] < x) left = mid + 1;
        else return mid;
    }
    return -1;
}
int BinarySearch_R(int* a, int x, int left, int right)
{
    if (left <= right)
    {
        int mid = (left + right) / 2;
        if (a[mid] > x) return BinarySearch_R(a, x, left, mid - 1);
        else if (a[mid < x]) return BinarySearch_R(a, x, mid + 1, right);
        else return mid;
    }
    return -1;
    
}
void test01()
{
    int a[] = { 1,2,3,4,5,6,7,8,9,10 };
    int num = 7;
    int result = BinarySearch_I(a, 10, num);
    if (result < 0)
        cout << "没找到！" << endl;
    else
        cout << "a[" << result << "} = " << num << endl;
}
void test02()
{
    int a[] = { 1,2,3,4,5,6,7,8,9};
    int num = 1;
    int right = sizeof(a) / sizeof(int);
    int result = BinarySearch_R(a,num,0,right);
    if (result < 0)
        cout << "没找到!" << endl;
    else
        cout<< "a[" << result << "} = " << num << endl;

}