CODEWITHSUNDEEP
java
aprdrivesmecrazy
aprdrivesmecrazy

Reputation: 99

How to properly handle max/min int value edge case-Java

I am working on a problem from LeetCode (not an interview question just practicing) that asks the following:

Given a sorted integer array nums, where the range of elements are in the inclusive range [lower, upper], return its missing ranges.

The code that I came up with fails for inputs where the nums array is [-2147483648,2147483647] and lower/upper are -2147483648/2147483647 respectively. The part of my code that actually answers the question is: 

if (nums[0]-lower > 1) {
    String range = lower + "->" + (nums[0]-1);
    ans.add(range);
}
else if (nums[0]-lower == 1) {
    String range = new Integer(lower).toString();
    ans.add(range);
}
for (int i = 1; i < nums.length; i++) {
        if (nums[i] - nums[i-1] > 2) {
            String range = nums[i-1]+1 + "->" + (nums[i]-1);
            ans.add(range);
        }
        else if (nums[i] - nums[i-1] == 2) {
            String range = new Integer(nums[i]-1).toString();
            ans.add(range);
        }
    }

I was wondering how best to handle this edge case, not just for this question but generally. Do I just add extra if-statements to my code to specifically handle these two numbers (or if addition/subtraction of numbers causes the int value to overflow) or is there a more elegant way to handle this?

Upvotes: 2

Views: 1319

Answers (1)

Erwin Bolwidt
Erwin Bolwidt

Reputation: 31279

The maximum value of an int is 231-1 which is 2147483647, but the difference between that number and any negative number is larger than that number itself.

So all your subtraction expressions like nums[0]-lower overflow with [-2147483648,2147483647] (or [-1,2147483647]).

You can check it with this:

System.out.println(2147483647 - -1);

This prints out -2147483648 even though you would expect it to be 2147483648.

One easy fix is to do the calculations as a 64-bit long. Change all your subtractions like below to cast the expression to long.

if (nums[0] - (long)lower > 1) {

Take the above example and change it to:

System.out.println(2147483647 - (long) -1);

This will correctly print 2147483648.

Upvotes: 5

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