Ural1225 (mathematics)

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Problem Solving Ideas:

On the first of the n is 1, 2, 3, 4 of the situation is roughly listed, found n = = 1 o'clock results for 2,n== 2 o'clock results of 2,n = = 3 o'clock results for 4,n== 4 o'clock result is 6.

So bold conjecture ans[i] = ans[i-1] + ans[i-2], but WA in #12. The preprocessing table out to see ... When N reaches 45, the result overflows, and the question long long does not exist, decisive open unsigned long long.

Full code:

#include <algorithm> #include <iostream> #include <cstring> #include <climits> #include < cstdio> #include <string> #include <cmath> #include <map> #include <queue>using namespace std ; typedef long long ll;const int MOD = int (1e9) +7;const int INF = 0x3f3f3f3f;const double EPS = 1e-9;const double PI = ACOs (-1.0); M_pi;int n;const int maxn = 55;unsigned Long Long ans[maxn];int main () {    #ifdef doubleq    freopen ("In.txt", "R", stdin);    #endif    Std::ios::sync_with_stdio (false);    Std::cin.tie (0);    ANS[1] = ans[2] = 2;    for (int i = 3; i < MAXN; i + +)        ans[i] = ans[i-1] + ans[i-2];    while (CIN >> N)    {        cout << ans[n] << Endl;    }}

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Ural1225 (mathematics)