Find Intersection Among Arrays

find-intersection-among-arrays.js

/*
ar : can be an array of arrays or an asssociative array

Examples:
================

intersect([[76,80,11,31,34,82,100], [13,31,66,43,73,100,73,10]])
will give [31,100]

intersect(
{
    colors1 : ['black', 'orange', 'white', 'blue', 'yellow'],
    colors2 : ['green', 'yellow', 'red', 'brown', 'black']
})
will give ['black', 'yellow']

intersect(
{
    colors1 : ['black', 'orange', 'white', 'blue', 'yellow'],
    colors2 : ['green', 'yellow', 'red', 'brown', 'black'],
    colors3 : ['yellow', 'red', 'pink', 'orange']
})
will give ['yellow']
*/
function intersect(ar)
{
    if (ar == null) return false;

    var a = new Array();

    if (ar.length == undefined) // Associative Array
    {
        for (var i in ar)
         a.push(ar[i]);
    }
    else
     a = ar;

    if (a.length == 1) return false; // Single array ? Nothing to intersect with

    var common = new Array();
    function loop(a, index, s_index, e_index)
    {
        if (index == null) index = 0;
        if (s_index == null) s_index = 0;
        if (e_index == null) e_index = a[index].length;
        if (index == a.length - 1) return;

        for (var i = s_index; i < e_index; i++)
        {
            if (common.indexOf(a[index][i]) != -1) continue;
            for (var j = 0; j < a[index + 1].length; j++)
            {
                if (a[index][i] != a[index+1][j]) continue;
                loop(a, index + 1, j, j + 1);
                if (index + 1 == a.length - 1) { common.push(a[index][i]); break; }
            }
        }
    }

    loop(a);
    return common;
}