TheAlgorithms/Java · error · IllegalArgumentException

Input array should have at least 2 distinct elements

Error message

Input array should have at least 2 distinct elements

What it means

Thrown by SecondMinMax (via private checkOutput) when the computed second-best still equals its initial sentinel (Integer.MAX_VALUE for min, Integer.MIN_VALUE for max). That happens only when no distinct second value exists, e.g., all elements are identical, because the second-best variable is never updated away from its initializer.

Source

Thrown at src/main/java/com/thealgorithms/maths/SecondMinMax.java:57

     */

    public static int findSecondMin(final int[] arr) {
        return secondBest(arr, Integer.MAX_VALUE, (a, b) -> a < b);
    }

    public static int findSecondMax(final int[] arr) {
        return secondBest(arr, Integer.MIN_VALUE, (a, b) -> a > b);
    }

    private static void checkInput(final int[] arr) {
        if (arr.length < 2) {
            throw new IllegalArgumentException("Input array must have length of at least two");
        }
    }

    private static void checkOutput(final int secNum, final int initialVal) {
        if (secNum == initialVal) {
            throw new IllegalArgumentException("Input array should have at least 2 distinct elements");
        }
    }
}

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Pre-filter the array to distinct values (e.g., via a Set) and verify at least 2 distinct elements remain before calling.
2. Treat 'all values equal' as a valid business outcome and wrap the call, returning the single value or an Optional.empty().
3. If duplicates are data errors, fix the upstream producer.

Example fix

// before
int second = SecondMinMax.findSecondMin(arr);

// after
long distinct = Arrays.stream(arr).distinct().count();
if (distinct < 2) {
    throw new IllegalStateException("Need >= 2 distinct values, found " + distinct);
}
int second = SecondMinMax.findSecondMin(arr);

long distinct = Arrays.stream(arr).distinct().count();
if (distinct < 2) {
    throw new IllegalStateException("Need >= 2 distinct values");
}
int s = SecondMinMax.findSecondMin(arr);

try {
    int s = SecondMinMax.findSecondMin(arr);
} catch (IllegalArgumentException e) {
    // all-equal is a valid state: return the single value or empty
    return arr.length > 0 ? OptionalInt.of(arr[0]) : OptionalInt.empty();
}

When it happens

Trigger: Call findSecondMin(new int[]{7,7,7}) or findSecondMax(new int[]{3,3}). Also triggered by an array of identical values, or an array whose distinct-element count is 1.

Common situations: Degenerate datasets where every sample is equal (constant sensor reading, single-value lookup table, a column of repeated defaults), or unit tests with simplistic fixtures.

Related errors

• k must be between 1 and the size of the array
• Array must be non-empty.
• Array must be non-empty.
• Array must be non-empty.
• array must be non-empty.

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/648e06ea4ceee17e. Report an issue: GitHub.