Multiply Strings

最新推荐文章于 2019-09-21 14:34:06 发布

原创最新推荐文章于 2019-09-21 14:34:06 发布 · 2k 阅读

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字符串 (string) 专栏收录该内容

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本文介绍了一种处理任意精度大数乘法的方法，通过将字符串形式的大整数转换为整型数组，再利用传统的乘法算法进行计算，并将结果转换回字符串形式返回。这种方法适用于超出常规整型变量表示范围的极大数值。

Given two numbers represented as strings, return multiplication of the numbers as a string.

Note: The numbers can be arbitrarily large and are non-negative.

public class Solution {
	public static void main(String[] args) {
		System.out.println(multiply("0", "0"));
	}
	
    public static String multiply(String num1, String num2) {
        if (num1 == null || num1.length() == 0 || num2 == null || num2.length() == 0) return "";
        int[] number1 = toIntegerArray(num1);
        int[] number2 = toIntegerArray(num2);
        int[] result = new int[num1.length() + num2.length()];
        
        int startIndex = 0;
        for (int i = num1.length() - 1; i >= 0; i--) {
            int extra = 0;
            for (int j = num2.length() - 1; j >= 0; j--) {
                int value = number1[i] * number2[j] + result[(result.length - 1) - startIndex + j - (num2.length() - 1)] + extra;
                extra = value / 10;
                value = value % 10;
                result[(result.length - 1) - startIndex + j - (num2.length() - 1)] = value;                
            }
            result[(result.length - 1) - startIndex -1 - (num2.length() - 1)] = extra;
            startIndex++;
        }
        String str = "";
        boolean isBeginningZero = true;
        for (int i = 0; i < result.length; i++) {
        	if (result[i] == 0 && isBeginningZero == true) {
        		
        	} else {
        		isBeginningZero = false;
        		str += result[i];
        	}
        }
        return str == "" ? "0" : str;
    }
    
    public static int[] toIntegerArray(String num) {
        if (num == null || num.length() == 0) return null;
        int length = num.length();
        int[] arr = new int[length];
        for (int i = 0; i < length; i++) {
            arr[i] = num.charAt(i) - '0';
        }
        return arr;
    }
}