leetcode 43. Multiply Strings | 43. 字符串相乘（Java）

题目

https://leetcode.com/problems/multiply-strings/

题解

模拟手动乘法，列竖式

class Solution {public String multiply(String num1, String num2) {// guarantee len(num1) > len(num2)if (num1.length() < num2.length()) {String t = num1;num1 = num2;num2 = t;}// simulate human multiplyString[] arr = new String[num2.length()];for (int i = num2.length() - 1, zero = 0; i >= 0; i--, zero++) {arr[i] = mul(num1, num2.charAt(i) - '0', zero);}StringBuilder result = new StringBuilder();int carry = 0;for (int i = arr[0].length() - 1; i >= 0; i--) {int cur = carry;for (String a : arr) {cur += a.charAt(i) - '0';}carry = cur / 10;result.insert(0, cur % 10);}// remove leading zerowhile (result.length() > 0 && result.charAt(0) == '0') {result.deleteCharAt(0);}return result.length() == 0 ? "0" : result.toString();}// 多位数 * 一位数public String mul(String num, int single, int zero) {StringBuilder result = new StringBuilder();int carry = 0;for (int i = num.length() - 1; i >= 0; i--) {int cur = carry + (num.charAt(i) - '0') * single;carry = cur / 10;result.insert(0, cur % 10);}if (carry > 0) result.insert(0, carry);return result.append("0".repeat(zero)).insert(0, "0".repeat(num.length() * 2 - result.length())).toString();}
}

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leetcode 43. Multiply Strings | 43. 字符串相乘（Java）

题目

题解

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