[leetcode]Palindrome Number

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Palindrome Number

Determine whether an integer is a palindrome. Do this without extra space.

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Some hints:

Could negative integers be palindromes? (ie, -1)

If you are thinking of converting the integer to string, note the restriction of using extra space.

You could also try reversing an integer. However, if you have solved the problem "Reverse Integer", you know that the reversed integer might overflow. How would you handle such case?

There is a more generic way of solving this problem.

演算法思路：

重點是求出該整數的位元！

 1 public class Solution { 2  public boolean isPalindrome(int x) { 3         if(x < 0) return false; 4         int n = x; 5         int length = 1; 6         while((n = n / 10) != 0) length++; 7         while(length > 1){ 8             int begin = x / pow(length); 9             int end = x % 10;10             if(begin != end) return false;11             x = (x - begin * pow(length)) / 10;12             length -= 2;13         }14         return true;15     }16     private int pow(int n){17         int result = 1;18         for(int i = 1; i < n; result *= 10,i++);19         return result;20     }21 }

不過這道題在leetcode上有專題講解，我不該班門弄斧的。時間複雜度O(length)，空間O(1)