[LeetCode 9] Palindrome Number

문제 바로가기

Description

---

Given an integer x, return true if x is a palindrome__, and false otherwise.

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

---

• -2^31 <= x <= 2^31 - 1

Hint

---

Hint 1

  Beware of overflow when you reverse the integer.
	

Code

---

내 제출

---

class Solution {
    public boolean isPalindrome(int x) {
        if (x < 0) { // 음수인 경우 false return
            return false;
        } else if (x == 0) {
            return true;
        } else if ((x % 10) == x) {
            return true;
        }
        
        // 문자열로 변환 후 대조
        String str = "" + x;
        char[] strs = str.toCharArray();

        int result = 0;
        int len = (int)Math.ceil((double)strs.length / 2); // result 값과 비교하여 true 반환

        for (int i = 0; i < len; i++) {
            for (int j = ((strs.length - 1) - i); j > 0; j--) {
                if (strs[i] == strs[j]) {
                    result++;
                    break;
                } else {
                    return false;
                }
            }
        }

        if (result == len) {
            return true;
        }
        return false;
    }
}

Runtime	Memory
7 ms	44.2 MB

다른 풀이

---

class Solution {
    public boolean isPalindrome(int x) {
        if (x < 0) {
            return false;
        }
        int q = 0, o = x;
        while (x > 0) {
            q = (x % 10) + q * 10;
            x = x / 10;
        }
        return q == o;
    }
}

Reference

---