#9.Palindrome Number
Problem statement
Given an integer x, return true if x is palindrome integer.
An integer is a palindrome when it reads the same backward as forward.
- For example,
121is a palindrome while123is not.
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.
Explanation
็ตฆๅฎไธๅ x ็ๆดๆธ๏ผๅฆๆๆฏๅๆๅ่ฟๅ true๏ผๅฆๅ false
ๅๆ็ๅฎ็พฉๆฏไธ่ซๅพ้ ญๆๅพๅฐพ้ๅง๏ผ่ฎ่ตทไพๆฏไธๆจฃ็๏ผไพๅฆ 121 ๅ 1221 ๆฏๅๆ๏ผไฝ 123 ไธๆฏ
Solution
้้ก่ฆ่ๆ ฎ็ๅฐๆนๆฏๅๆ็้ทๅบฆ๏ผๅถๆธ้ทๅบฆ็ๅๆๅๅฒ็บๅทฆๅณๅ ฉ็ญๅๆๆฏ่ผๅฅฝๅคๆท๏ผๅฅๆธ้ทๅบฆ็ๅๆๆๅพๆ็ไธไธญ้็ๆธ๏ผๅฎไธ้่ๅ ถไปๆธๅฐๆ๏ผไธ้ก็ฎๆๅพ็ Follow up ้ๆๅฐ่ฝๅฆๅจไธๅฐๆธๅญ่ฝๆๆๅญไธฒ็ๆ ๆณไธไพ่งฃ๏ผไพ็ งๅ่ฟฐ็ๅๆๅ้กๆ๏ผๆญค้กๅฏไฝฟ็จ็ฎ่ก้็ฎๅญ๏ผArithmetic operators๏ผไพ่งฃใ
ไธ้ๅงๅ ้ๆฟพไธไบ็นๅฎ็ๆขไปถ
- ๅคๆท
xๆฏๅฆ็บ 0๏ผๅฆๆๆฏ return true - ๅคๆท
xๆฏๅฆๅฐๆผ 0 ๆ่ ็บ 10 ็ๅๆธ๏ผๅฆๆๆฏ return false
ๆฅ่ๅท่ก while ่ฟดๅ็ดๅฐๆขไปถๆ็ซ๏ผๆๅพ return x ่ๆทๅๅบ็ reverseNum ๆฏๅฆ็ธ็ญใ
public bool IsPalindrome(int x)
{
if (x == 0)
return true;
if (x < 0 || x % 10 == 0)
return false;
int reverseNum = 0;
while (x > reverseNum)
{
reverseNum = reverseNum * 10 + x % 10;
x /= 10;
}
return x == reverseNum || x == reverseNum / 10;
}
Reference
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