var generate = function(numRows) {
    // helper function that takes in the last level and then constructs the next level
    // takes in an array, spits out an array
    // sums i and i+1 , careful with the end length - 2
    var helper = function (arr) {
        var newArr = [1];
        for (var i = 0; i < arr.length - 1; i++) {
            newArr.push(arr[i] + arr[i+1]);
        }
        newArr.push(1);
        return newArr;
    }

    //initialize tree
    var result = [];
    var currentArr = [1];

    //for loop that loops through all levels
    for (var j = 0; j < numRows; j++) {
        result.push(currentArr);
        currentArr = helper(currentArr);
    }
    return result;
};