TheAlgorithms/Java · error · IllegalArgumentException

Invalid range indices

Error message

Invalid range indices

What it means

Thrown by RangeSumQuery.sumRange(prefixSum, left, right) when the range is invalid: left < 0, right >= prefixSum.length - 1, or left > right. Note this throws IllegalArgumentException (not IndexOutOfBoundsException like PrefixSum.sumRange does) — an inconsistency between the two classes. Bounds are inclusive and measured against the ORIGINAL array length (prefixSum.length - 1).

Source

Thrown at src/main/java/com/thealgorithms/prefixsum/RangeSumQuery.java:69

        return prefixSum;
    }

    /**
     * Returns the sum of elements from index left to right (inclusive)
     * using the provided prefix sum array.
     *
     * @param prefixSum The prefix sum array computed using buildPrefixSum.
     * @param left      The start index (inclusive).
     * @param right     The end index (inclusive).
     * @return The sum of elements in the range [left, right].
     * @throws IllegalArgumentException if indices are invalid.
     */
    public static int sumRange(int[] prefixSum, int left, int right) {
        if (prefixSum == null) {
            throw new IllegalArgumentException("Prefix sum array cannot be null");
        }
        if (left < 0 || right >= prefixSum.length - 1 || left > right) {
            throw new IllegalArgumentException("Invalid range indices");
        }
        return prefixSum[right + 1] - prefixSum[left];
    }
}

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Remember prefixSum has length n+1: valid right is at most prefixSum.length - 2 for a data array of size n.
2. Track the ORIGINAL data length separately and validate right < dataLength.
3. Use the PrefixSum class instead, which encapsulates the length and avoids this confusion.

Example fix

// before
int s = RangeSumQuery.sumRange(ps, left, right); // right miscomputed against ps.length

// after
int s = RangeSumQuery.sumRange(ps, left, Math.min(right, ps.length - 2)); // data length = ps.length - 1

int dataLen = prefixSum.length - 1; // prefix array is n+1
if (left < 0 || right >= dataLen || left > right) {
    throw new IllegalArgumentException("range invalid for data length " + dataLen);
}
int s = RangeSumQuery.sumRange(prefixSum, left, right);

static boolean validStaticRange(int left, int rightInclusive, int prefixArrayLength) {
    int dataLen = prefixArrayLength - 1;
    return left >= 0 && rightInclusive < dataLen && left <= rightInclusive;
}

try {
    int s = RangeSumQuery.sumRange(prefixSum, left, right);
} catch (IllegalArgumentException e) {
    logger.warn("Bad static range query");
}

When it happens

Trigger: Call sumRange(ps, 0, ps.length - 1) treating the prefix array's own length as the data length; sumRange(ps, -1, 2); sumRange(ps, 5, 2).

Common situations: Confusing the prefix-sum array length (n+1) with the data length (n); passing an exclusive end as inclusive; 1-based indices not converted.

Related errors

• Invalid range: [%d, %d] for array of size %d
• Input array cannot be null or empty.
• Input array cannot be null
• Invalid range indices
• Input matrix cannot be null or empty

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/830af27fbd0e87cd. Report an issue: GitHub.