Difficulty: Medium
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:
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Input: num1 = "2", num2 = "3"
Output: "6"
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Example 2:
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Input: num1 = "123", num2 = "456"
Output: "56088"
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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.
Solution
Language: Java
乘法的过程
num1[i] * num2[j] 的结果将会落在 [i + j, i + j + 1]
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class {
public String multiply(String num1, String num2) {
if (num1 == null || num2 == null || num1.length() == 0 || num2.length() == 0
|| num1.equals("0") || num2.equals("0")) {
return "0";
}
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();
}
}
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