[leetcode note] Palindrome Number

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时间: 2019-10-12 12:03 AM
题目地址: https://leetcode.com/problems/palindrome-number/

Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.

判断是否为回文数字

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.

Solution 1:

public boolean isPalindrome(int x) {
    if(x < 0 || (x % 10 == 0 && x != 0)) {
        return false;
    }
    int y = 0;
    while(x > y) {
        y = y * 10 + x % 10;
        x /= 10;
    }
    return x == y || x == y / 10;
}

Runtime: 7 ms, faster than 65.57% of Java online submissions for Palindrome Number.
Memory Usage: 36.1 MB, less than 5.02% of Java online submissions for Palindrome Number.

Solution 2:

public boolean isPalindrome(int x) {
    if(x < 0 || (x % 10 == 0 && x != 0)) {
        return false;
    }
    char[] chars = String.valueOf(x).toCharArray();
    int start = 0;
    int end = chars.length - 1;
    while(start < end) {
        if (chars[start++] != chars[end--]) {
            return false;
        }
    }
    return true;
}

Runtime: 8 ms, faster than 40.24% of Java online submissions for Palindrome Number.
Memory Usage: 36.3 MB, less than 5.02% of Java online submissions for Palindrome Number.

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