//顺序查找，查找成功返回下标，否则返回-1；
int sequentialSearch(int r[],int len,int key)
{
    if(len <= 0){
        return -1;
    }

    for(int i = 0;i < len;i++){
        if(r[i] == key){
            return i;
        }
    }

    return -1;
}

//折半查找
int binarySearch(int r[],int low,int high,int key)
{
    int mid;

    while (low <= high) {
        mid = (low + high)/2;

        if(r[mid] == key){
            return mid;
        }

        if(r[mid] > key){
            high = mid - 1;
        }else{
            low = mid + 1;
        }
    }

    return -1;
}

//折半查找，递归实现
int binarySearchRec(int r[],int low,int high,int key)
{
    if(low > high){
        return -1;
    }
    int mid = (low + high) / 2;

    if(r[mid] == key){
        return mid;
    }

    if(r[mid] > key){
        return binarySearchRec(r,low,mid - 1,key);
    }else{
        return binarySearchRec(r,mid + 1,high,key);
    }

    return -1;
}