ForHosting KIT · Developer Utilities

Monotone lattice paths on an a×b grid

This lattice path counter returns how many monotone routes travel from the origin (0, 0) to the grid point (a, b) using only right steps and up steps.

● BetaFree · in your browser

Run — free How it works & API

Use it from WebAPIEmailTelegramApp soon

That classic combinatorics count equals the binomial coefficient C(a + b, a), which is the same as C(a + b, b), because every path is a sequence of exactly a east moves and b north moves. Familiar checks include a two-by-two square with six paths, a two-by-three rectangle with ten paths, and a degenerate corridor with zero width where the only route is a single vertical climb. The engine evaluates the binomial with a deterministic BigInt product, so large grids keep every digit instead of sliding into floating-point noise. There are no network calls, no Monte Carlo samples, and no date-based shortcuts. Explore free in the browser for homework, contest prep, and coding kata, or call the API at $0.002 per successful request when you need reproducible lattice-path fixtures in CI, teaching worksheets, or demos of binomial grid geometry.

How to use it

Enter your values in the form above. The tool checks them before calculating and shows the result on the same page.

Check your inputs

Use the labels and units shown next to each field. If something is missing or outside the allowed range, the page points to the field to fix.

Use it again or automate it

Use the browser tool for individual checks and the API when you need the same capability in an automated workflow.

What you can do with it

Get an answer now

Enter one set of values and see the result without building a spreadsheet or script.

Compare scenarios

Change one value at a time and rerun the calculation to understand what affects the result.

Automate repeated work

Use the API when the same calculation needs to run inside your product or workflow.

FAQ

How do I use this capability?

Complete the fields above and run it on this page. The form highlights anything that needs attention.

For developers — API access

Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.

API endpoint

POSThttps://api.kit.forhosting.com/combo/lattice-paths

Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.

Call it from your stack

curl -X POST https://api.kit.forhosting.com/combo/lattice-paths \
  -H "Authorization: Bearer $KIT_KEY" \
  -H "Content-Type: application/json" \
  -d '{"a":2,"b":3}'

const res = await fetch("https://api.kit.forhosting.com/combo/lattice-paths", {
  method: "POST",
  headers: {
    "Authorization": `Bearer ${process.env.KIT_KEY}`,
    "Content-Type": "application/json"
  },
  body: JSON.stringify({
    "a": 2,
    "b": 3
  })
});
const { task_id } = await res.json();

import os, requests

res = requests.post(
    "https://api.kit.forhosting.com/combo/lattice-paths",
    headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
    json={
    "a": 2,
    "b": 3
},
)
task_id = res.json()["task_id"]

<?php
$res = file_get_contents("https://api.kit.forhosting.com/combo/lattice-paths", false, stream_context_create([
  "http" => [
    "method"  => "POST",
    "header"  => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
    "content" => '{"a":2,"b":3}',
  ],
]));
$task = json_decode($res, true);

body := bytes.NewBufferString(`{"a":2,"b":3}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/combo/lattice-paths", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)

Example request

{
  "a": 2,
  "b": 3
}

Example response

{
  "task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
  "type": "combo.lattice_paths",
  "status": "queued",
  "_links": {
    "result": "/tasks/tsk_…/result"
  }
}

The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.

Pricing

Per request$0.002

Published price — no tokens, no invented credits. A failed task is never charged.

Limits

`max_a`	500
`max_b`	500

Errors

HTTP	Code	Meaning
`401`	`unauthorized`	Missing or invalid API key.
`402`	`insufficient_balance`	Your balance doesn't cover the task price.
`404`	`unknown_type`	That task type doesn't exist.
`429`	`rate_limited`	Too many requests. Use the webhook instead of polling.

Read the full KIT documentation →

Run — free