做題筆記：Palindrome Number (Java)
題目描述：
給定一個整數 x，如果 x 是回文數，則返回 true。
回文數指一個整數向後讀和向前讀內容相同。
Example 1:
Input: x = 121
Output: true
Explanation: 121 reads as 121 from left to right and from right to left.Example 2:
Input: x = -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: x = 10
Output: false
Explanation: Reads 01 from right to left. Therefore it is not a palindrome.算術解法：
利用 Java 整數倒序計算：
class Solution {
public boolean isPalindrome(int x) {
if (x < 0) {
return false;
}
int ori = x;
int p = 0;
while (ori != 0) {
p = p * 10 + ori % 10;
ori /= 10;
}
return x == p;
}
}9 ms，超過 87.67% 的答案。
轉換為 String 的解法：
進階要求 Follow Up 竟然問了一句 Could you solve it without converting the integer to a string? 原來我想到的已經是進階方法了，常規解法是轉換為 String：
class Solution {
public boolean isPalindrome(int x) {
char[] nums = String.valueOf(x).toCharArray();
int start = 0;
int end = nums.length-1;
while(start < end) {
if(nums[start] != nums[end]) return false;
start++; end--;
}
return true;
}
}19 ms，超過 19.48% 的答案。