Zibx

var calculate = function( arr ){ // one cycle solution
    var minMax, 
        sum = 0, 
        fullSum = 0,
        el, 
        maxMax,
        i, _i = arr.length - 1;
        
    minMax = arr[0]; // first item is the current left max
    maxMax = arr[_i]; // last item is the current right max