用栈非递归实现fib数列

#include <bits/stdc++.h>
using namespace std;
struct node
{
    int val;
    int tag;
    node(int a = 0, int b = 0) : val(a), tag(b){}
};
long long fib(int x)
{
    stack<node> s;
    long long sum = 0;
    do
    {
        while (x > 2)
        {
            s.push(node(x, 1));
            x--;
        }
        sum++;
        while (!s.empty())
        {
            node temp = s.top(); s.pop();
            if (temp.tag == 1)
            {
                temp.tag = 2;
                s.push(temp);
                x = temp.val - 2;
                break;
            }
        }
    } while (!s.empty());
    return sum;
}

int main()
{
    int v[100];
    v[1] = v[2] = 1;
    for (int i = 3; i <= 20; i++)
        v[i] = fib(i);
    for (int i = 1; i <= 20; i++)
        cout << v[i] << endl;
}