• https://leetcode.com/problems/multiply-strings/
• 43. Multiply Strings

JavaScript 解答

var multiply = function (num1, num2) {
    var m = num1.length;
    var n = num2.length;
    var arr = new Array(m + n).fill(0);
    for (var i = m - 1; i >= 0; i--) {
        for (var j = n - 1; j >= 0; j--) {
            var mul = (num1[i] - '0') * (num2[j] - '0');

            var sum = mul + arr[i + j + 1];

            arr[i + j] += Math.floor(sum / 10);
            arr[i + j + 1] = sum % 10;
        }
    }

    var str = arr.reduce((a, b) => {
        if (a === '' && b === 0) return a;
        return a + b;
    }, '');

    return str ? str : '0';

};

Ruby 解答

def multiply(num1, num2)
  (integer_of(num1.chars.map { |i| i.ord - 48 }) * integer_of(num2.chars.map { |i| i.ord - 48 })).to_s
end

def integer_of(digits)
  result = 0
  digits.each do |d|
    result *= 10
    result += d
  end
  result
end