二分查找、三分查找求极点、二分求等比数列【模板】

二分查找：

int a[110],N;
int BinarySearch(int *a,int x)
{
    int Left = a[1];
    int Right = a[N];
    while(Left <= Right)
    {
        int mid = (Left+Right)>>1;
        if(a[mid] == x)
            return mid;
        else if(a[mid] > x)
            Right = mid - 1;
        else
            Left = mid + 1;
    }
    return -1;
}

三分查找求极点：

double left,right,mid,midmid;
left = 0;
right = PI/2;
while(right-left >= 1e-7)
{
    mid = (left+right)/2;
    midmid = (mid+right)/2;
    if(calc(mid) > calc(midmid))
        right = midmid;
    else
        left = mid;
}  

二分求等比数列

LL Power(LL p,LL n)
{
    LL ret = 1;
    while(n > 0)
    {
        if(n&1)
            ret = ret * p % 9901;
        p = p * p % 9901;
        n >>= 1;
    }
    return ret;
}  

LL Sum(LL p,LL n)  //递归二分求(1 + p^1 + p^2 + … + p^n)%mod
{
    if(n == 0)
        return 1;  

    if(n&1)
        return (Sum(p,n/2)*(1+Power(p,n/2+1)))%9901;
    else
        return (Sum(p,n/2-1)*(1+Power(p,n/2+1)) + Power(p,n/2))%9901;  

}