LeetCode Top Interview 150

Richard20122023-11-13 10:08

Math

Q****9. Palindrome Number

Given an integer x, return trueif x is a palindrome, and false otherwise.

Example 1:

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Input: x = 121
Output: true
Explanation: 121 reads as 121 from left to right and from right to left.

Example 2:

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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:

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

Constraints:

-231 <= x <= 231 - 1

Follow up: Could you solve it without converting the integer to a string?

解法及注释:

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class Solution {    public boolean isPalindrome(int x) {        //pre-check        if(x < 0 || x > Math.pow(2,31)-1 || (x != 0 && x %10 == 0 )) {            return false;        }        if(x < 10) {            return true;        }         return useString(x);        //return useMath(x);    }    private boolean useString(int x) {        String s = String.valueOf(x);        int n = s.length();        for(int i = 0; i < n/2; i++) {            if(s.charAt(i) != s.charAt(n-i-1)) {                return false;            }        }        return true;    }    private boolean useMath(int x) {        int rev = 0;        while(x > rev) {            rev = rev * 10 + x % 10;            x /= 10;        }        return (x == rev || x == rev/10);     }}