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[Leetcode]9. Palindrome Number(C++)

题目描述

题目链接:9. Palindrome Number

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

例子

例子 1

Input: 121
Output: true

例子 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.

例子 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?

解题思路

首先如果不是正数可以直接返回结果(负数为 false,0 为 true),正数的情况通过求余从个位开始赋值到另一个整型最后判断两数是否相等即可。注意由于翻转的时候 int 可能放不下,所以存翻转值的类型需要是 long。代码如下:

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class Solution {
public:
bool isPalindrome(int x) {
if (x < 0) return false;
if (x == 9) return true;
long x1 = 0;
int copy = x;
while (x > 0) {
x1 *= 10;
x1 += x % 10;
x /= 10;
}
return x1 == copy;
}
};
  • 时间复杂度: O(digits of x)
  • 空间复杂度: O(1)

GitHub 代码同步地址: 9.PalindromeNumber.cpp

其他题目:
GitHub: Leetcode-C++-Solution
博客: Leetcode-Solutions