Search found 215 matches

by ImLazy
Thu Sep 20, 2007 8:34 am
Forum: Volume 112 (11200-11299)
Topic: 11275 - 3D Triangles
Replies: 6
Views: 3862

My AC code's epsilon is 1e-8. Your algorithm is right, but notice the problem statement: "if the distance between two points is equal or less than 1e-6, they are regarded as one point". So you should consider these situations: 1. If the distance between one endpoint of triangle A and one edge of tri...
by ImLazy
Wed Sep 12, 2007 2:37 am
Forum: Algorithms
Topic: Whether a 3D vector is on the clockwise side of another one
Replies: 1
Views: 1457

Oh, I'm so stupid, there is no clockwise in 3-dimension coordinate system.
Sorry.
by ImLazy
Tue Sep 11, 2007 5:32 pm
Forum: Algorithms
Topic: Whether a 3D vector is on the clockwise side of another one
Replies: 1
Views: 1457

Whether a 3D vector is on the clockwise side of another one

I know for two 2-dimension vectors u and v, calculate the cross product of u and v. if it is positive,then u is on the clockwise side of v.
How to extend this problem to 3 dimension?
by ImLazy
Mon Jul 16, 2007 1:13 pm
Forum: Algorithms
Topic: Get the maximun product.
Replies: 4
Views: 2141

OK, the second problem is a little bit different, but I'm trying to understand it.
Thanks.
by ImLazy
Mon Jul 16, 2007 12:50 pm
Forum: Algorithms
Topic: Get the maximun product.
Replies: 4
Views: 2141

Oh, thank you. You described it very clearly.
But a further question:
It is said when dividind X into n parts, and X1 must not be less than A (A > X / n), then the optimal partition is X1 = A, X2 = X3 ... = Xn = (X - A) / (n - 1).
Is it true?
by ImLazy
Mon Jul 16, 2007 8:22 am
Forum: Algorithms
Topic: Get the maximun product.
Replies: 4
Views: 2141

Get the maximun product.

It is said if you want to divide a positive number X to n parts, X1, X2 ... Xn, that X1 + X2 ... + Xn = X, and make their product X1 * X2 ... * Xn maximun, you should divide X averagely, i.e. X1 = X2 = ... = Xn = (X / n).
Is it true? If any, can anybody prove it for me.
Thanks.
by ImLazy
Sun Jul 15, 2007 6:24 am
Forum: Volume 111 (11100-11199)
Topic: 11107 - Life Forms
Replies: 21
Views: 13882

I couldn't find a more efficient algorithm, but unfortunately I get a 'memory limit exceeded'. Any idea ?? To avoid MLE, you should not copy the substrings to other places, but just reference the pointers of their original places. And don't use STL string for this problem, but use the C style strin...
by ImLazy
Thu Jun 28, 2007 12:30 pm
Forum: C++
Topic: Why can we use the manipulators in <iomanip>
Replies: 3
Views: 2090

Oh, I see. The manipulators in <iomanip> don't use the overloads of operator << in <ostream>, but the overloads defined in <iomanip> which are not visible for us. Am I right?
by ImLazy
Thu Jun 28, 2007 8:25 am
Forum: C++
Topic: Why can we use the manipulators in <iomanip>
Replies: 3
Views: 2090

Why can we use the manipulators in <iomanip>

It is said the manipulators in the header <iomanip> can be used in the operator <<, such as: cout << setbase(16) << 100 << endl; But when I read the manual of the header <iomanip>, here , I found none of the manipulators receives argument of type ios_base. So I can't understand which overload of ope...
by ImLazy
Wed Dec 27, 2006 7:29 am
Forum: C++
Topic: Why we can use "while(cin >> a)"
Replies: 6
Views: 3255

Yes, I find it in the basic_ios.h.

Code: Select all

/**
 *  @brief  The quick-and-easy status check.
 *
 *  This allows you to write constructs such as
 *  "if (!a_stream) ..." and "while (a_stream) ..."
*/
operator void*() const
{ return this->fail() ? 0 : const_cast<basic_ios*>(this); }
by ImLazy
Mon Dec 18, 2006 4:05 pm
Forum: C++
Topic: A class with static member function. Compile error.
Replies: 2
Views: 1915

Thank you.
by ImLazy
Mon Dec 18, 2006 2:14 pm
Forum: C++
Topic: A class with static member function. Compile error.
Replies: 2
Views: 1915

A class with static member function. Compile error.

This is my code: #include <iostream> using namespace std; class A { private: static int a; public: static void set(int i) { a = i; } static void get() { cout << a << endl; } }; int main() { A::set(199); A::get(); return 0; } This is the compiling result: /tmp/ccaeaQQB.o: In function `A::set(int)': s...
by ImLazy
Tue Oct 17, 2006 5:02 am
Forum: C++
Topic: Is a class implicitly a friend class of itself?
Replies: 5
Views: 2947

Watch the function "f()" in my first post. It changes the value of a variable in another object. I think it's strange. I typed another code and it get compilation error. #include <iostream> using namespace std; class B { private: int i; }; class A { public: void f(B& b) { b.i++; cout << b.i << endl;...
by ImLazy
Fri Oct 13, 2006 6:16 am
Forum: C++
Topic: STL :: sort + binary search for character array!
Replies: 2
Views: 2079

Elements to be sorted by "sort()" must has an "<" operator. I don't know how to sort a 2-dimension array. Maybe you should put your string in to an structure. Like this code: struct MyStr { char str[100]; bool operator < (const MyStr& s) const { return strcmp(str, s.str) < 0; } }; main() { MyStr str...
by ImLazy
Wed Oct 11, 2006 12:00 pm
Forum: C++
Topic: Is a class implicitly a friend class of itself?
Replies: 5
Views: 2947

Is a class implicitly a friend class of itself?

Watch this code: #include <iostream> using namespace std; class A { private: int i; public: A() { i = 0; } void f(A& a) { a.i++; cout << a.i << endl; } }; int main() { A a, b; a.f(b); return 0; } It is accepted by the compiler(g++ 4.1.0). I think it's strange. A class can access the member variable ...

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