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43. multiply strings 实现参考

admin 11月 14, 2020 0

Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2, also represented as a string.

Example 1:

1 2	Input: num1 = "2", num2 = "3" Output: "6"

Example 2:

1 2	Input: num1 = "123", num2 = "456" Output: "56088"

Note:

The length of both num1 and num2 is < 110.
Both num1 and num2 contain only digits 0-9.
Both num1 and num2 do not contain any leading zero, except the number 0 itself.
You must not use any built-in BigInteger library or convert the inputs to integer directly.

字符串相乘

实现

java

public static String (String num1, String num2) {
    int m = num1.length(), n = num2.length();
    int[] pos = new int[m + n];
    for(int i = m - 1; i >= 0; i--) {
      for(int j = n - 1; j >= 0; j--) {
        int mul = ( num1.charAt(i) - '0' ) * ( num2.charAt(j) - '0' );
        int p1 = i + j, p2 = i + j + 1;
        int sum = mul + pos[p2];
        pos[p1] += sum / 10;
        pos[p2] = sum % 10;
      }
    }
    StringBuilder sb = new StringBuilder();
    for(int p: pos) {
      if(!( sb.length() == 0 && p == 0 )) {
        sb.append(p);
      }
    }
    return sb.length() == 0 ? "0" : sb.toString();
  }

参考

multiply-strings