[codeforces 516]A. Drazil and Factorial
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[codeforces 516]A. Drazil and Factorial
试题描述
Drazil is playing a math game with Varda.
Let‘s define for positive integer x as a product of factorials of its digits. For example, .
First, they choose a decimal number a consisting of n digits that contains at least one digit larger than 1. This number may possibly start with leading zeroes. Then they should find maximum positive number x satisfying following two conditions:
1. x doesn‘t contain neither digit 0 nor digit 1.
2. = .
Help friends find such number.
输入
The first line contains an integer n (1 ≤ n ≤ 15) — the number of digits in a.
The second line contains n digits of a. There is at least one digit in a that is larger than 1. Number a may possibly contain leading zeroes.
输出
输入示例
4 1234
输出示例
33222
数据规模及约定
见“输入”
题解
这个题相当有意思,我看 n 那么小,那一定是 dp 了,然而写完了才发现 F(a) 会爆 long long,所以只好另辟蹊径。后来发现一个性质:只要把 a 的每一位数都尽量的分出最多数出来,然后再拼到一起就好了,这个不难证明,就是个贪心,若将两个数的阶乘合并成一个数的阶乘,则答案会减少 1,一定不优。
现在的任务是把 2, 3, 4, ... , 9 这些 1 位数尽量多地分解,我发现刚刚的 dp 没有白写:
#include <iostream> #include <cstdio> #include <algorithm> #include <cmath> #include <stack> #include <vector> #include <queue> #include <cstring> #include <string> #include <map> #include <set> using namespace std; const int BufferSize = 1 << 16; char buffer[BufferSize], *Head, *Tail; inline char Getchar() { if(Head == Tail) { int l = fread(buffer, 1, BufferSize, stdin); Tail = (Head = buffer) + l; } return *Head++; } int read() { int x = 0, f = 1; char c = getchar(); while(!isdigit(c)){ if(c == ‘-‘) f = -1; c = getchar(); } while(isdigit(c)){ x = x * 10 + c - ‘0‘; c = getchar(); } return x * f; } #define maxn 6000010 #define maxk 20 int n, sum, fact[maxk], F[maxn], f[maxn][11]; char num[maxk]; bool vis[maxn]; bool Less(int* a, int* b) { for(int i = 9; i >= 2; i--) if(a[i] != b[i]) return a[i] < b[i]; return 0; } int main() { n = read(); scanf("%s", num + 1); fact[0] = 1; for(int i = 1; i <= 9; i++) fact[i] = fact[i-1] * i; sum = 1; for(int i = 1; i <= n; i++) sum *= fact[num[i]-‘0‘]; vis[1] = 1; for(int i = 1; i <= sum; i++) if(vis[i]) { // printf("%d ", i); for(int k = 2; k <= 9 && fact[k] * i <= sum; k++) { int t = fact[k] * i; // printf("[%d]", t); vis[t] = 1; if(F[t] < F[i] + 1) { F[t] = F[i] + 1; memcpy(f[t], f[i], sizeof(f[i])); f[t][k]++; } if(F[t] > F[i] + 1) continue; f[i][k]++; if(Less(f[t], f[i])) memcpy(f[t], f[i], sizeof(f[i])); f[i][k]--; } } for(int i = 9; i >= 2; i--) for(int j = 1; j <= f[sum][i]; j++) putchar(i + ‘0‘); putchar(‘\n‘); return 0; }
就依次输入,结果记一下,在主程序中打个表:
#include <iostream> #include <cstdio> #include <algorithm> #include <cmath> #include <stack> #include <vector> #include <queue> #include <cstring> #include <string> #include <map> #include <set> using namespace std; const int BufferSize = 1 << 16; char buffer[BufferSize], *Head, *Tail; inline char Getchar() { if(Head == Tail) { int l = fread(buffer, 1, BufferSize, stdin); Tail = (Head = buffer) + l; } return *Head++; } int read() { int x = 0, f = 1; char c = getchar(); while(!isdigit(c)){ if(c == ‘-‘) f = -1; c = getchar(); } while(isdigit(c)){ x = x * 10 + c - ‘0‘; c = getchar(); } return x * f; } #define maxn 20 int n, cnt[maxn]; char num[maxn]; int main() { n = read(); scanf("%s", num + 1); for(int i = 1; i <= n; i++) { if(num[i] == ‘9‘) { cnt[7]++; cnt[3]++; cnt[3]++; cnt[2]++; } if(num[i] == ‘8‘) { cnt[7]++; cnt[2]++; cnt[2]++; cnt[2]++; } if(num[i] == ‘7‘) { cnt[7]++; } if(num[i] == ‘6‘) { cnt[5]++; cnt[3]++; } if(num[i] == ‘5‘) { cnt[5]++; } if(num[i] == ‘4‘) { cnt[3]++; cnt[2]++; cnt[2]++; } if(num[i] == ‘3‘) { cnt[3]++; } if(num[i] == ‘2‘) { cnt[2]++; } } for(int i = 7; i >= 2; i--) for(int j = 1; j <= cnt[i]; j++) putchar(i + ‘0‘); putchar(‘\n‘); return 0; }
A 啦!
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