Max Subsequence Sum

maxSubsequence.js

var xs = [-4,-3,-7,+2,+1,-1,-4],    //[2,1] = 3
    ys = [-2,11,-4,13,-5,-2],      //[11,-4,13] = 20
    zs = [5,15,-30,10,-5,40,10,-8] //   [...] = 55

function sum(j,as){
    var max = Math.max;
    function tabulate(i,runMax,curMax){
        if(i > j) return curMax
        var newMax = max(runMax+as[i],as[i])
        return tabulate(i + 1, newMax, max(curMax,newMax))
    }
    
    return j == 0 ? as[0] : tabulate(1,as[0],as[0])
}

sum(6,xs) //3
sum(5,ys) //20
sum(7,zs) //55