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/*

* Copyright(c) 2019 Jiau Zhang

* For more information see <https://github.com/JiauZhang/algorithms>

*

* This repo is free software: you can redistribute it and/or modify

* it under the terms of the GNU General Public License as published by

* the Free Software Foundation

*

* It is distributed in the hope that it will be useful,

* but WITHOUT ANY WARRANTY; without even the implied warranty of

* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

* GNU General Public License for more details.

*

* You should have received a copy of the GNU General Public License

* along with THIS repo. If not, see <http://www.gnu.org/licenses/>.

*/

#include <iostream>

#include <list>

using namespace std;

/************************* soulution-1 **************************/

class add {

public:

add() { sum = sum + n; n++; }

//a static data member that can only be initialized at its definition

static int sum;

static int n;

static int getSum() { return sum; }

};

int add::sum = 0;

int add::n = 1;

int accumulate_1(int n)

{

add *sum = new add[n];

delete[] sum;

sum = NULL;

return add::getSum();

}

/************************* soulution-2 **************************/

class End;

End *end_start[2];

class End {

public:

virtual int sum(int n) {

return 0;

}

};

class Start: public End {

virtual int sum(int n) {

// n 非零时执行当前函数递归，

// 为零时实行父类函数，其直接返回，扮演终止条件

return end_start[!!n]->sum(n-1) + n;

}

};

int accumulate_2(int n)

{

if (n<1)

return -1;

End e;

Start s;

end_start[0] = &e;

end_start[1] = &s;

return end_start[!!n]->sum(n);

}

/************************* soulution-3 **************************/

typedef int (*func)(int n);

int Stop(int n)

{

return 0;

}

int Begin(int n)

{

static func f[2] = {Stop, Begin};

return f[!!n](n-1) + n;

}

int accumulate_3(int n)

{

return Begin(n);

}

/************************* soulution-4 **************************/

template <int n>

struct solution4 {

enum Value {

sum = solution4<n-1>::sum + n

};

};

template <>

struct solution4<1> {

enum Value {

sum = 1

};

};

int accumulate_4(int n)

{

const int m = 10;

struct solution4<m> s;

return s.sum;

}

int main(int argc, char **argv)

{

cout << accumulate_1(10) << endl;

cout << accumulate_2(10) << endl;

cout << accumulate_3(10) << endl;

cout << accumulate_4(10) << endl;

}