7. Reverse Integer [LeetCode]

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本文介绍两个经典算法题目：整数反转与判断回文数。整数反转需注意处理溢出情况；判断回文数则通过反转整数并与原数比较来实现。两题均采用C语言实现。

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7. Reverse Integer

/**************************************************************************
 * 
 * 7. [Reverse Integer](https://leetcode.com/problems/reverse-integer/)
 * 
 * Given a 32-bit signed integer, reverse digits of an integer.
 * if outside the signed 32-bit integer range [-231, 231 - 1], then return 0
 * 
 * Example:
 *  123 =>  321
 * -123 => -321
 *  120 =>   21
 * -2147483648 => 0
 **************************************************************************/

int reverse(int x){
    long long num = x;
    long long res = 0;

    for ( ; num; num/=10)
        res = res*10 + num % 10;
    
    if (res > INT_MAX || res < INT_MIN)
        return 0;
    else
        return res;
}

9. Palindrome Number



/**************************************************************************
 * 
 * 9. [Palindrome Number](https://leetcode.com/problems/palindrome-number/)
 * 
 * Given an integer x, return true if x is palindrome integer. 
 * An integer is a palindrome when it reads the same backward as forward. 
 * For example, 121 is palindrome while 123 is not.
 * 
 * Example 1:
 * Input: x = 121
 * Output: true
 * 
 * Example 2:
 * Input: x = -121
 * Output: false
 * 
 * Example 3:
 * Input: x = 10
 * Output: false
 **************************************************************************/


bool isPalindrome(int x){
    if (x < 0) return false;
    long long ret = 0;
    for (int num = x; num; num/=10)
        ret = ret * 10 + num % 10;
    if (ret > INT_MAX) return false;
    return ret == x;
}