java大数相乘算法

ゝ一世哀愁。 2022-07-16 02:14 198阅读 0赞

public class MyMultiply {
    
    	/**
    	 * @param args
    	 */
    	public static void main(String[] args) {
    		// System.out.println("Hello world");
    
    		//String str1 = "1234";
    		//String str2 = "1234";
    		//String str1 = "1076060999";
    		//String str2 = "90188905567";
    		String str1 = "23456789009877666555544444";
    		String str2 = "346587436598437594375943875943875";
    
    		int len1 = str1.length();
    		int len2 = str2.length();
    
    		char[] s1 = str1.toCharArray();
    		char[] s2 = str2.toCharArray();
    
    		// 高低位对调
    		covertdata(s1, len1);
    		covertdata(s2, len2);
    
    		System.out.println("乘数："+str1);
    		System.out.println("乘数："+str2);
    		multiply(s1, len1, s2, len2);
    
    	}
    
    	public static void covertdata(char data[], int len) {
    		//高低位对调
    		for (int i = 0; i < len / 2; i++) {
    			data[i] += data[len - 1 - i];
    			data[len - 1 - i] = (char) (data[i] - data[len - 1 - i]);
    			data[i] = (char) (data[i] - data[len - 1 - i]);
    		}
    	}
    
    	public static void multiply(char a[], int alen, char b[], int blen) {
    		// 两数乘积位数不会超过乘数位数和+ 3位
    		int csize = alen + blen + 3;
    		// 开辟乘积数组
    		int[] c = new int[csize];
    		// 乘积数组填充0
    		for (int ii = 0; ii < csize; ii++) {
    			c[ii] = 0;
    		}
    		// 对齐逐位相乘
    		for (int j = 0; j < blen; j++) {
    			for (int i = 0; i < alen; i++) {
    				c[i + j] +=  Integer.parseInt(String.valueOf(a[i]))* Integer.parseInt(String.valueOf(b[j]));
    			}
    		}
    		int m = 0;
    		// 进位处理
    		for (m = 0; m < csize; m++) {
    			int carry = c[m] / 10;
    			c[m] = c[m] % 10;
    			if (carry > 0)
    				c[m + 1] += carry;
    		}
    		// 找到最高位
    		for (m = csize - 1; m >= 0;) {
    			if (c[m] > 0)
    				break;
    			m--;
    		}
    		// 由最高位开始打印乘积
    		System.out.print("乘积：");
    		for (int n = 0; n <= m; n++) {
    			System.out.print(c[m - n]);
    		}
    		System.out.println("");
    	}
    }