TheAlgorithms/Go · error

can't have a negative n-th catalan number

Error message

can't have a negative n-th catalan number

What it means

A package-level sentinel (errCatalan) returned by NthCatalanNumber when n < 0; Catalan numbers are only defined for non-negative indices, so this generic negative-argument guard rejects the offending n.

Source

Thrown at dynamic/catalan.go:11

//The Catalan numbers are a sequence of positive integers that appear in many counting
// problems in combinatorics.
// time complexity: O(n²)
// space complexity: O(n)
//reference: https://brilliant.org/wiki/catalan-numbers/

package dynamic

import "fmt"

var errCatalan = fmt.Errorf("can't have a negative n-th catalan number")

// NthCatalan returns the n-th Catalan Number
// Complexity: O(n²)
func NthCatalanNumber(n int) (int64, error) {
	if n < 0 {
		//doesn't accept negative number
		return 0, errCatalan
	}

	var catalanNumberList []int64
	catalanNumberList = append(catalanNumberList, 1) //first value is 1

	for i := 1; i <= n; i++ {
		catalanNumberList = append(catalanNumberList, 0) //append 0 and calculate

		for j := 0; j < i; j++ {
			catalanNumberList[i] += catalanNumberList[j] * catalanNumberList[i-j-1]
		}

View on GitHub (pinned to 5ba447ec5f)

Solutions

1. Validate n>=0 before calling
2. Return 0 for negative n at the call site if a default is acceptable
3. Compare with errors.Is(err, errCatalan) to handle specifically

When it happens

Trigger: Thrown at dynamic/catalan.go:11 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of TheAlgorithms/Go@5ba447ec5f (2026-09-02). Data as JSON: /api/errors/cdf5ea1168e3419b. Report an issue: GitHub.