Poj 2853,2140 Sequence Sum Possibilities(因式分解)
一、Description
Most positive integers may be written as a sum of a sequence of at least two consecutive positive integers. For instance,
6 = 1 + 2 + 3 9 = 5 + 4 = 2 + 3 + 4but 8 cannot be so written.
Write a program which will compute how many different ways an input number may be written as a sum of a sequence of at least two consecutive positive integers.
Input
The first line of input will contain the number of problem instances N on a line by itself, (1
≤ N ≤ 1000) . This will be follo
wed by N lines, one for each problem instance. Each problem line will have the problem number, a single space and the number to be written as a sequence of consecutive positive integers. The second number will be less than 231 (so will fit
in a 32-bit integer).
Output
The output for each problem instance will be a single line containing the problem number, a single space and the number of ways the input number can be written as a sequence of consecutive positive integers.
二、题解
一种解法:
1. 这串连续的整数可以表示为:(x+1)+(x+2)+(x+3)+(x+4)+……+(x+i) , 其中x=0,1,2 ......
2. 假设已经找到:(x+1)+(x+2)+(x+3)+(x+4)+……+(x+i) =number;
3. A=number-(1+2+3+......+i)=number-(1+i)*i/2;
4. A=x*i;即A一定能被i整除,从而达到判定目的.
三、java代码
import java.util.Scanner; public class Main { public static void main(String[] args) { Scanner sc=new Scanner(System.in); int i,j,n,num,sum,temp; n=sc.nextInt(); for(i=0;i<n;i++){ num=sc.nextInt(); sum=0; temp=sc.nextInt(); for(j=2;(j+1)*j/2<=temp;j++){ if((temp-(j+1)*j/2)%j==0) sum++; } System.out.println(num+" "+(sum)); } } }
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