Multiply Strings LeetCode solution in Java

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class Solution {
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  public String multiply(String num1, String num2) {
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    if (num1.equals("0") || num2.equals("0")) return "0";
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    int[] arr = new int[num1.length() + num2.length()];
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    int index = 0;
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    for (int i = num1.length() - 1; i >= 0; i--) {
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      int carry = 0;
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      int column = 0;
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      for (int j = num2.length() - 1; j >= 0; j--) {
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        int a = (num1.charAt(i) - '0') * (num2.charAt(j) - '0');
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        int temp = (arr[index + column] + carry + a);
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        arr[index + column] = temp % 10;
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        carry = temp / 10;
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        column++;
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      }
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      if (carry != 0) {
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        arr[index + column] = carry;
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      }
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      index++;
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    }
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    String ans = "";
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    index = arr.length - 1;
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    while (arr[index] == 0) {
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      index--;
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    }
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    for (int i = index; i >= 0; i--) {
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      ans += arr[i];
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    }
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    return ans;
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  }
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}