43. 字符串相乘

浅浅的花香味﹌ 2023-10-04 08:01 16阅读 0赞

给定两个以字符串形式表示的非负整数 `num1` 和 `num2`，返回 `num1` 和 `num2` 的乘积，它们的乘积也表示为字符串形式。

**示例 1:**

输入: num1 = "2", num2 = "3"
    输出: "6"

**示例 2:**

输入: num1 = "123", num2 = "456"
    输出: "56088"

**说明：**

1.  `num1` 和 `num2` 的长度小于110。
2.  `num1` 和 `num2` 只包含数字 `0-9`。
3.  `num1` 和 `num2` 均不以零开头，除非是数字 0 本身。
4.  **不能使用任何标准库的大数类型（比如 BigInteger）**或**直接将输入转换为整数来处理**。

public class Solution43 {
    	public String multiply(String num1, String num2) {
    		String out = "";
    		String sum = "";
    		String temp = "";
    		int n1 = 0;
    		int n2 = 0;
    		int n3 = 0;
    		int n4 = 0;
    
    		for (int i = num1.length() - 1; i > -1; i--) {
    			n1 = Integer.parseInt(num1.substring(i, i + 1));
    			temp = "";
    			n4 = 0;
    			for (int j = num2.length() - 1; j > -1; j--) {
    				n2 = Integer.parseInt(num2.substring(j, j + 1));
    //				System.out.println("n1=" + n1);
    //				System.out.println("n2=" + n2);
    				n3 = n1 * n2 + n4;
    				if (n3 >= 10) {
    					n4 = n3 / 10;
    					n3 = n3 % 10;
    				} else {
    					n4 = 0;
    				}
    				temp = n3 + temp;
    //				System.out.println("n3=" + n3);
    //				System.out.println("n4=" + n4);
    			}
    			if (n4 > 0) {
    				temp = n4 + temp;
    			}
    //			System.out.println("temp=" + temp);
    			for (int z = 0; z < num1.length() - 1 - i; z++) {
    				temp = temp + "0";
    			}
    //			System.out.println("temp=" + temp);
    			sum = addStrings(temp, sum);
    		}
    //		System.out.println("sum=" + sum);
    		out=sum;
    		int len = sum.length();
    		for (int i = 0; i < len; i++) {
    			if (sum.substring(i, i + 1).equals("0")) {
    				out = sum.substring(i);
    			} else {
    				break;
    			}
    		}
    		return out;
    	}
    
    	public String addStrings(String num1, String num2) {
    		String out = "";
    		int l1 = num1.length();
    		int l2 = num2.length();
    		if (l1 > l2) {
    			for (int i = 0; i < l1 - l2; i++) {
    				num2 = "0" + num2;
    			}
    		}
    		if (l2 > l1) {
    			for (int i = 0; i < l2 - l1; i++) {
    				num1 = "0" + num1;
    			}
    		}
    //		System.out.println(num1);
    //		System.out.println(num2);
    		int n1 = 0;
    		int n2 = 0;
    		int n3 = 0;
    		int n4 = 0;
    		for (int i = num1.length() - 1; i > -1; i--) {
    			n1 = Integer.parseInt(num1.substring(i, i + 1));
    			n2 = Integer.parseInt(num2.substring(i, i + 1));
    			n3 = n1 + n2 + n4;
    			if (n3 >= 10) {
    				n4 = 1;
    				n3 = n3 - 10;
    			} else {
    				n4 = 0;
    			}
    			out = n3 + out;
    //			System.out.println(n3);
    //			System.out.println(n4);
    		}
    		if (n4 == 1) {
    			out = n4 + out;
    		}
    		return out;
    	}
    
    	public static void main(String[] args) {
    
    		Solution43 sol = new Solution43();
    
    		String num1 = "2";
    		String num2 = "3";
    
    		System.out.println(sol.multiply(num1, num2));
    	}
    }