LEETCODE算法:9. Palindrome Number

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题目

Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.

Example 1:

Input: 121 Output: true Example 2:

Input: -121 Output: false Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome. Example 3:

Input: 10 Output: false Explanation: Reads 01 from right to left. Therefore it is not a palindrome. Follow up:

Coud you solve it without converting the integer to a string?

题解

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//转换字符串
class Solution {
public:
    bool isPalindrome(int x) {
        if(x<0) return false;
        string tmp=to_string(x);
        int i=0,j=tmp.length()-1;
        while(i<=j)
        {
            if(tmp[i]!=tmp[j]) return false;
            i++;j--;
        }
        return true;
    }
};
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//翻转后一半的数字，然后通过比较大小的方式确定是否为回文数，要排除末尾为0的te
class Solution {
public:
    bool isPalindrome(int x) {
        if(x<0) return false;
        else if(x!=0&&x%10==0) return false;
        int rev=0;
        while(rev<x)
        {
            rev=rev*10+x%10;
            x/=10;
        }
        return rev==x||(rev/10)==x;
    }
};