[TOC]

P009 Palindrome Number

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

思路分析

• 负数==>false
• 从两头对数字逐渐切割，一旦有不同的==>false

代码

java

public class Solution009 {
    public boolean isPalindrome(int x) {
        if (x < 0)
            return false;
        else if (x <= 9)
            return true;

        int base = 1;
        // 取得最高位的级数base=power(10,n)
        while (x / base >= 10)
            base *= 10;
        while (x != 0) {
            int left = x / base;
            int right = x % 10;
            if (left != right)
                return false;
            x -= base * left;// 去掉最高位
            x /= 10;// 去掉最低位
            base /= 100;// 去掉了两位数,base/100
        }
        return true;
    }
}

python

class Solution009(object):
    def isPalindrome(self, x):
        """
        :type x: int
        :rtype: bool
        """
        
        if x < 0:return False
        elif x <= 9 :return True
        
        base = 1
        
        while x / base >= 10:
            base *= 10
        
        while x != 0:
            l = x / base
            r = x % 10
            if l != r:return False
            
            x -= l * base
            x /= 10
            base /= 100
        
        return True