大整数相乘算法

Java代码

1. package cn.bigint;
3. import java.io.IOException;
5. public class BigInts {
6. public String BigIntAdd(String s1, String s2) throws IOException {
7. IntString intt1 = new IntString();
8. String str = "";
9. IntString intt2 = new IntString();
10. intt1.digits = convert(s1);
11. intt1.len = s1.length();
12. intt2.digits = convert(s2);
13. intt2.len = s2.length();
14. int[] a = intt1.digits;
15. int[] b = intt2.digits;
16. int alength = intt1.len;
17. int blength = intt2.len;
18. IntString intt3 = new IntString();
19. intt3.len = (alength + blength);
20. int clength = intt3.len;
21. int[] c = new int[clength];
22. for (int i = 0; i < alength; ++i) {
23. for (int j = 0; j < blength; ++j) {
24. c[(i + j)] += a[i] * b[j];
25. }
26. }
28. for (int i = 0; i < c.length; ++i) {
29. if (c[i] > 9) {
30. c[(i + 1)] += c[i] / 10;
31. c[i] %= 10;
32. }
33. }
35. intt3.digits = c;
37. clength = intt3.len;
39. if (c[(clength - 1)] ==0)
40. --clength;
41. for (int i = clength -1; i >= 0; --i) {
42. str = str + String.valueOf(c[i]);
43. }
44. return str;
45. }
47. public static int[] convert(String str) {
48. int length = str.length();
50. int[] t = new int[length];
52. for (int i = 0; i < str.length(); ++i) {
53. t[i] = (str.charAt(length - i - 1) - '0');
54. }
55. return t;
56. }
58. class IntString {
59. public int len;
60. public int[] digits;
62. public IntString() {
63. this.len = 0;
65. this.digits = null;
66. }
67. }