1009. Product of Polynomials (25)

This time, you are supposed to find A*B where A and B are two polynomials.

Input Specification:

Each input file contains one test case. Each case occupies 2 lines, and each line contains the information of a polynomial: K N1 a_N1 N2 a_N2 ... NK a_NK, where K is the number of nonzero terms in the polynomial, Ni and a_Ni (i=1, 2, ..., K) are the exponents and coefficients, respectively. It is given that 1 <= K <= 10, 0 <= NK < ... < N2 < N1 <=1000.

 

Output Specification:

For each test case you should output the product of A and B in one line, with the same format as the input. Notice that there must be NO extra space at the end of each line. Please be accurate up to 1 decimal place.

Sample Input

2 1 2.4 0 3.2
2 2 1.5 1 0.5

Sample Output

3 3 3.6 2 6.0 1 1.6

和1002題很是相似，仍然是利用hash思想存儲AB兩個多項式，找出其中的非零項相乘併合併到結果數組result中的。值得注意的是result的最大指數是2000，而不是加法中的1000。

PS：能夠根據讀入的最大指數去分配數組的內存，減小佔用空間。

 1 import java.util.*;
 2 
 3 public class Main {
 4 
 5     public static void main(String[] args) {
 6         float[] A = new float[1001];
 7         float[] B = new float[1001];
 8         float[] result = new float[2001];
 9         Scanner in = new Scanner(System.in);
10         int K1 = in.nextInt();
11         for (int i = 0; i < K1; i++) {
12             A[in.nextInt()] = in.nextFloat();
13         }
14         int K2 = in.nextInt();
15         for (int i = 0; i < K2; i++) {
16             B[in.nextInt()] = in.nextFloat();
17         }
18         for (int i = 0; i < 1001; i++) {
19             if (A[i] != 0) {
20                 for (int j = 0; j < 1001; j++) {
21                     if (B[j] != 0) {
22                         result[i + j] += A[i] * B[j];
23                     }
24                 }
25             }
26         }
27 
28         StringBuilder sb = new StringBuilder();
29         int count = 0;
30         for (int i = 2000; i >= 0; i--) {
31             if (result[i] != 0) {
32                 count++;
33                 sb.append(String.format(" %d %.1f", i, result[i]));
34             }
35         }
36         System.out.println(count + sb.toString());
37 
38     }
39 }