[Go] LeetCode 7. Reverse Integer

Description

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

This solution code includes 3 steps.

1. pop operation
2. check beforehand whether or not appending push ope would cause overflow.
3. push operation

/* [Go] Approach 1: Pop and Push Digits & Check before Overflow */
//MaxInt32 == 32767
func reverse(x int) int {
    var rev int
    for x != 0 {
        //1.pop operation
        pop := x % 10
        x /= 10
        
        //2.check beforehand whether or not appending push ope would cause overflow.
        if ( rev > math.MaxInt32/10 || (rev == math.MaxInt32/10 && pop > 7)){
            return 0
        }
        if ( rev < math.MinInt32/10 || (rev == math.MinInt32/10 && pop < -8)){
            return 0
        }
        
        //3. push operation
        rev = rev * 10 + pop
    }
    return rev
}