Given an integer x, return true if x is a palindrome, and false otherwise.
palindrome: An integer is a palindrome when it reads the same forward and backward. For example, 121 is a palindrome while 123 is 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.
Constraints:
Follow up: Could you solve it without converting the integer to a string?
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class Solution:
def isPalindrome(self, x: int) -> bool:
rev = 0
y = x
while y > 0:
rev = rev * 10 + y % 10
y //= 10
return rev == x
'''
Reverse only half
'''
class Solution:
def isPalindrome(self, x: int) -> bool:
if x < 0 or (x % 10 == 0 and x != 0):
return False
rev = 0
while x > rev:
rev = rev * 10 + x % 10
x //= 10
return x == rev or x == rev // 10
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func isPalindrome(x int) bool {
if x < 0 || (x % 10 == 0 && x != 0) {
return false
}
revNum := 0
for x > revNum {
revNum = revNum * 10 + x % 10
x /= 10
}
return x == revNum || x == revNum/10
}
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class Solution {
public boolean isPalindrome(int x) {
if (x < 0 || (x % 10 == 0 && x != 0)) {
return false;
}
int reverted = 0;
while (x > reverted) {
reverted = reverted * 10 + x % 10;
x /= 10;
}
return x == reverted || x == reverted / 10;
}
}
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