LeetCode 9. Palindrome Number

最新推荐文章于 2022-04-02 15:31:39 发布

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本文介绍了两种不使用额外空间的方法来判断整数是否为回文数：直接处理整数和将其转换为字符串进行比较。

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

Easy to make mistakes.....

There are more than two ways to handle it.

// Handle integer as an integer.

   int integerMask(int x) {
        int mask = 1;
        while(x / 10 > 0) {
            mask = mask * 10;
            x = x / 10;
        }
        return mask;
    }
    bool isPalindrome(int x) {
        if(x < 0) return false;    // if negative, it is absolutely not palindrome then.
        int mask = integerMask(x);
        while(x > 0) {
            if(x % 10 != (x / mask)) return false;
            x = x % mask;
            x = x / 10;
            mask = mask / 100;
        }
        return true;
    }

// Change the integer into string type.

    bool isPalindrome(string x) {
        int i = 0;
        int j = x.size() - 1;
        while(i < j) {
            if(x[i] != x[j]) return false;
            i++;
            j--;
        }
        return true;
    }
    bool isPalindrome(int x) {
        string tmp = to_string(x);
        return isPalindrome(tmp);
    }