简单二分

#include <iostream>

using namespace std;
//upper_bound(a, arr + 10, 7) - a;
int search(int *a, int l, int r, int key)
{
    int mid;
    while(l <= r)
    {
        mid = (l + r) / 2;
        if(a[mid] == key) return mid;
        if(a[mid] < key) l = mid + 1;
        if(a[mid] > key) r = mid - 1;
    }
    return -1;
}
int upper_bound(int *a, int l, int r, int key)
{
    int mid;
    while(l <= r)
    {
        mid = (l + r) / 2;
        if(a[mid] <= key) l = mid + 1;
        if(a[mid] > key) r = mid - 1;
    }
    return -1;
}

int main()
{
    int a[] = {1,2,3,3,4,6,7,7,8,8,9};
    int l = 0, r = 10;
    int key;
    cin >> key;
    int pos = search(a,l,r,key);
    cout << "key:" << "a" << "[" << pos << "]" << endl;
    return 0;
}