[LeetCode 9] Palindrome Number

[Problem Link]

Description

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

Example

Input: 121
Output: true

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.

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

Solution 1

class Solution {
public:
    bool isPalindrome(int x) {
        string temp;
        stringstream ss;
        ss << x;
        ss >> temp;
        if (!isdigit(temp[0])) return false;
        int ssLen = temp.length();
        for (int i = 0; i < ssLen/2 + 1; i++) {
            if (temp[i] != temp[ssLen-i-1]) return false;
        }
        return true;
    }
};

Solution 2

class Solution {
public:
    bool isPalindrome(int x) {
        if (x < 0) return false;
        long firstVal = x;
        long secondVal = 0;
        while(x != 0) {
            secondVal = secondVal*10 + x%10;
            x = x/10;
        }
        cout << secondVal;
        if (firstVal != secondVal) return false;
        return true;
    }
};

Summary

• 解法1將int轉爲字符串解決。
• 解法2沒利用字符串解決，計算出倒序的數值再進行比較。