用C++编译器优化实现记忆化

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如果要实现输出fib(100)%1200007，可以实现用编译器来自动记忆化。

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#include<iostream>
using namespace std;
template<int x>
struct fib{
	static const int val = (fib<x - 1>::val + fib<x - 2>::val) % 1200007;
}
template<>
struct fib<0>{
	static const int val = 1;
}
template<>
struct fib<1>{
	static const int val = 1;
}
int main(){
	cout << fib<100>::val << endl;
	return 0;
}

编译器在编译的时候就会对这个进行优化，会非常快速算出来。

【工程代码】

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#include <iostream>
using namespace std;

template<int x>
struct fib{
    static const int val = (fib<x - 1>::val + fib<x - 2>::val) % 1200007;
};

template<>
struct fib<0>{
    static const int val = 0;
};

template<>
struct fib<1>{
    static const int val = 1;
};

int fib2(int x){
    if (x < 2) return x;
    else return (fib2(x - 1) + fib2(x - 2)) % 1200007;
}

int fib3(int x){
    int a = 0, b = 1,c;
    if (x == 0) b = 0;
    else if (x == 1) b = 1;
    else{
        for (int i = 2; i <= x; i++)
        {
            c = a + b;
            a = b;
            b = c % 1200007;
        }
    }
    return b;
}

class fib4{
    int *nums;
    bool *labels;
    int n;
    int calc(int x){
        if (labels[x]) return nums[x];
        nums[x] = calc(x - 1) + calc(x - 2);
        labels[x] = 1;
        return nums[x] % 1200007;
    }
public:
    fib4(int x){
        n = x;
        nums = new int [n];
        labels = new bool [n];
        memset(labels, 0, sizeof(char) * n);
        labels[0] = labels[1] = 1;
        nums[0] = 0;
        nums[1] = 1;
    }
    int getFib(){
        return calc(n);
    }
};
int main(){
    cout << fib<100>::val << endl;
    cout << fib3(100) << endl;
    fib4 f = fib4(100);
    cout << f.getFib() << endl;
    return 0;
}