TheAlgorithms/Go · error

left boundary starts from the first node

Error message

left boundary starts from the first node

What it means

Singly.CheckRangeFromIndex enforces that positions are 1-based node positions, matching ReversePartition's convention that the first node is position 1. A left of 0 or negative would corrupt the traversal (e.g. seeking to a node before the head), so it is rejected with this error.

Source

Thrown at structure/linkedlist/singlylinkedlist.go:167

	pre := tmpNode
	for i := 0; i < left-1; i++ {
		pre = pre.Next
	}
	cur := pre.Next
	for i := 0; i < right-left; i++ {
		next := cur.Next
		cur.Next = next.Next
		next.Next = pre.Next
		pre.Next = next
	}
	ll.Head = tmpNode.Next
	return nil
}
func (ll *Singly[T]) CheckRangeFromIndex(left, right int) error {
	if left > right {
		return errors.New("left boundary must smaller than right")
	} else if left < 1 {
		return errors.New("left boundary starts from the first node")
	} else if right > ll.length {
		return errors.New("right boundary cannot be greater than the length of the linked list")
	}
	return nil
}

// Display prints out the elements of the list.
func (ll *Singly[T]) Display() {
	for cur := ll.Head; cur != nil; cur = cur.Next {
		fmt.Print(cur.Val, " ")
	}

	fmt.Print("\n")
}

View on GitHub (pinned to 5ba447ec5f)

Solutions

1. Convert 0-based indexes to 1-based by adding 1 before the call
2. Clamp: if left < 1 { left = 1 }
3. Validate user input so positions are at least 1

Example fix

// before
ll.ReversePartition(i, j) // i, j are 0-based
// after
ll.ReversePartition(i+1, j+1) // convert to 1-based node positions

if left < 1 {
    return errors.New("positions are 1-based; left must be >= 1")
}
ll.ReversePartition(left, right)

if err := ll.CheckRangeFromIndex(left, right); err != nil {
    return fmt.Errorf("invalid range: %w", err)
}

When it happens

Trigger: Calling ReversePartition(left, right) with left < 1 — typically passing a 0-based index into this 1-based API, or a computed offset that went negative.

Common situations: Mixing 0-based array indexing habits with this 1-based list API; subtracting from a position without a floor check; deserialized positions starting at 0.

Related errors

• left boundary must smaller than right
• right boundary cannot be greater than the length of the link
• index out of range
• index out of range
• index out of bounds

AI-assisted analysis of TheAlgorithms/Go@5ba447ec5f (2026-09-02). Data as JSON: /api/errors/1b8c0086804779f8. Report an issue: GitHub.