[Luogu] P1255 数楼梯

Luogu P1255 数楼梯

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传送门

递推公式：\(F[i] = F[i - 1] + F[i - 2]\)，\(2 \leqslant i \leqslant n\)。

初始化\(F[0] = F[1] = 1\)即可。

数据太大，记得高精

#include <cstdio>
const int MAXN = 5001;
int n;
int f[MAXN][1100];
inline void print(int *x) {
    for (int i = x[0]; i >= 1; --i)
        printf("%d", x[i]);
    printf("\n");
    return ;
}
inline void sum(int *a, int *b, int *c) {
    int len = b[0] > c[0] ? b[0] : c[0];
    for (int i = 1; i <= len; ++i) {
        a[i] = a[i] + b[i] + c[i];
        if(a[i] >= 10) a[i + 1] = a[i] / 10, a[i] = a[i] % 10;
    }
    a[0] = a[len + 1] ? len + 1 : len;
    return ;
}
int main() {
    scanf("%d", &n);
    if(n == 0) {printf("0\n"); return 0;}
    f[0][1] = f[0][0] = f[1][1] = f[1][0] = 1;
    for (int i = 2; i <= n; ++i)
        sum(f[i], f[i - 1], f[i - 2]);
    print(f[n]);
    return 0;
}