mathball/lib/bell/index.js

A JavaScript library for Competitive Programming

'use strict';

function _toConsumableArray(arr) { if (Array.isArray(arr)) { for (var i = 0, arr2 = Array(arr.length); i < arr.length; i++) { arr2[i] = arr[i]; } return arr2; } else { return Array.from(arr); } }

/* N-th bell Number
 * Function: bell()
 */

var validate = require('../validation/non-negative-integer');

function bell(number) {

    var bell = [].concat(_toConsumableArray(Array(number + 1))).map(function (x) {
        return Array(number + 1).fill(0);
    });

    bell[0][0] = 1;

    for (var i = 1; i <= number; i++) {
        var temp = bell[i - 1][i - 1];
        bell[i][0] = temp;

        for (var j = 1; j <= i; j++) {
            var t1 = bell[i - 1][j - 1];
            var t2 = bell[i][j - 1];
            bell[i][j] = t1 + t2;
        }
    }
    var v = bell[number][0];
    return v;
}

exports.find = function (num) {

    validate(num, 'bell');

    return bell(num);
};