leoschur

/**
* group an array by accessor
* @param arr array of elements
* @param accessor called on element, must return a value from the elements after which they are to be grouped
* @returns Map where keys are defined by accessor function and values are an array of elements
*/
const groupBy = (a, accessor) => {
    if (!Array.isArray(a)) throw 'param a is not an array';
    if (typeof(accessor) != 'function') throw 'param accessor is not a function';
    return a.reduce(

leoschur

function sqm(base, exponent, mod) {
    let ze = 1; let a = base;
    while (exponent) {
        if (exponent & 1) ze = (ze * a) % mod;
        a = (a * a) % mod;
        exponent = exponent >> 1;
        // console.log("Ze: " + ze + " A: " + a);
    }
    return ze;
}