javaLogic errorMedium

Midpoint integer overflow in binary search

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What it should do

Calculate midpoint between two array indices. Example: computeMidpointIndex(10, 20) -> 15

What happens instead

(low + high) / 2 overflows to negative number when sum exceeds Integer.MAX_VALUE

public class Main {
    public static int computeMidpointIndex(int low, int high) {
        // (low + high) overflows 32-bit signed integer when sum > 2,147,483,647
        return (low + high) / 2;
    }

    public static void main(String[] args) {
        System.out.println(computeMidpointIndex(10, 20));
    }
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

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This bug belongs to the logic errors pattern

The wrong operator, an inverted condition, a formula the right way round but backwards.

Learn the logic errors pattern Step through your own code

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public class Main { public static int computeMidpointIndex(int low, int high) { // (low + high) overflows 32-bit signed integer when sum > 2,147,483,647 return (low + high) / 2; } public static void main(String[] args) { System.out.println(computeMidpointIndex(10, 20)); } }

Midpoint integer overflow in binary search

What it should do

What happens instead

More logic errors to practise

Midpoint integer overflow in binary search

What it should do

What happens instead

More logic errors to practise