7. Reverse Integer

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Given a 32-bit signed integer, reverse digits of an integer.

Example 1:

Input: 123
Output: 321

Example 2:

Input: -123
Output: -321

Example 3:

Input: 120
Output: 21

Note: Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [−231, 231 − 1]. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

Solution

這題不難，但要注意overflow的判定，目前看到比較好的做法是透過long去存reverse結果，若發現overflow int的範圍就傳回0

public int reverse(int x) {
        long ret = 0;
        
        while(x != 0){
            ret = ret*10 + (x%10);
            x = x/10;
            if( ret > Integer.MAX_VALUE || ret < Integer.MIN_VALUE)
                return 0;
        }
        return (int)ret;
    }