LeetCode 9. Palindrome Number
9.Palindrome Number
Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.
Example 1:
Input: 121
Output: true
Example 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.
Example 3:
Input: 10
Output: false
Explanation: Reads 01 from right to left. Therefore it is not a palindrome.
求出回文数对比
将数字反转进行对比。可以参考LeetCode 7。
public boolean isPalindrome(int x) {
if(x < 0){
return false;
}
int res = 0;
int y = x;
while(y != 0){
res = res* 10 + (y % 10);
y = y/10;
}
return x==res;
}
数字转字符串
将数字转换成字符串，然后使用两个指针左右进行对比。不过这样做效率很低。因为还要考虑数字转字符串的成本。
if(x < 0 || x >= Integer.MAX_VALUE){
return false;
}
String s = String.valueOf(x);
int len = s.length();
int left = 0;
int right = len -1;
while(left < right){
if(s.charAt(left) != s.charAt(right)){
return false;
}
left++;
right--;
}
return true;
}
right--;
}
return true;
}