Consider this sequence {1, 2, 3, . . . , N}, as a initial sequence of first N natural numbers. You canearrange this sequence in many ways. There will be N! different arrangements. You have to calculatethe number of arrangement of first N natural numbers…
题意:给定 n,m,k,问你在 1 ~ n 的排列中,前 m 个恰好有 k 个不在自己位置的排列有多少个. 析:枚举 m+1 ~ n 中有多少个恰好在自己位置,这个是C(n-m, i),然后前面选出 k 个,是C(m, k),剩下 n - k - i 个是都不在自己位置,也就是错排 D[n-k-i],求一个和就Ok了. 代码如下: #pragma comment(linker, "/STACK:1024000000,1024000000") #include <cstdio>…
UVA 10539 - Almost Prime Numbers 题目链接 题意:给定一个区间,求这个区间中的Almost prime number,Almost prime number的定义为:仅仅能整除一个素数. 思路:既然是仅仅能整除一个素数,那么这些数肯定为素数的x次方(x > 1),那么仅仅要先打出素数表,然后在素数表上暴力找一遍就能够了,由于素数表仅仅要找到sqrt(Max),大概100W,然后每一个数找的复杂度为log(n),这样复杂度是能够接受的. 代码: #include <…
1095 - Arrange the Numbers Consider this sequence {1, 2, 3 ... N}, as an initial sequence of first N natural numbers. You can rearrange this sequence in many ways. There will be a total of N! arrangements. You have to calculate the number of arrangem…
A palindrome is a word, number, or phrase that reads the same forwards as backwards. For example,the name “anna” is a palindrome. Numbers can also be palindromes (e.g. 151 or 753357). Additionallynumbers can of course be ordered in size. The first few…
