Leetcode 537. Complex Number Multiplication

Given two strings representing two complex numbers.

You need to return a string representing their multiplication. Note i2 = -1 according to the definition.

Example 1:

Input: "1+1i", "1+1i"
Output: "0+2i"
Explanation: (1 + i) * (1 + i) = 1 + i2 + 2 * i = 2i, and you need convert it to the form of 0+2i.

Example 2:

Input: "1+-1i", "1+-1i"
Output: "0+-2i"
Explanation: (1 - i) * (1 - i) = 1 + i2 - 2 * i = -2i, and you need convert it to the form of 0+-2i.

Note:

1. The input strings will not have extra blank.
2. The input strings will be given in the form of a+bi, where the integer a and b will both belong to the range of [-100, 100]. And the output should be also in this form.

Code (Java):

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class Solution {     public String complexNumberMultiply(String a, String b) {         // parse the r and i         //         String delim = "[+]";         String[] tokensA = a.split(delim);         String[] tokensB = b.split(delim);           // get real part         //         int r1 = getInteger(tokensA[0]);         int r2 = getInteger(tokensB[0]);           // get imiminary part         //         int i1 = getInteger(tokensA[1].substring(0, tokensA[1].length() - 1));         int i2 = getInteger(tokensB[1].substring(0, tokensB[1].length() - 1));           // compose the result         //         int r3 = r1 * r2 - i1 * i2;         int i3 = r1 * i2 + r2 * i1;           return r3 + "+" + i3 + "i";     }       private int getInteger(String s) {         boolean isNeg = false;         int i = 0;         if (s.charAt(0) == '-') {             isNeg = true;             i++;         }           int result = 0;         while (i < s.length()) {             int digit = Character.getNumericValue(s.charAt(i));             result = result * 10 + digit;             i++;         }           if (isNeg) {             result = -result;         }           return result;     } }