osigmao的专栏

注意dividend是0的情况，这个时候sum总是比被除数大的！尼玛考虑负数的情况！而且还有溢出的情况。。。。 -（-2147483648）溢出啦 亲。。。要从O(n) -> O(lgn) -> O(1)

1. x == reverse(x)?2. public class Solution { // 1. could negative number be Palindrome? // 2. reverse Integer! public boolean isPalindrome(int x) { if (x < 0) return false

You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a link

1, 考虑溢出 -》用long。 If the correct value is out of the range of representable values, INT_MAX (2147483647) or INT_MIN (-2147483648) is returned.2，

public class Solution { public String multiply(String num1, String num2) { if (num1 == null || num2 == null) { return null; } int len1 = num1.length(); int l