Alexandroppolus

function getHeightRec(arr, height1, height2, max) {
    if (arr.length === 0) {
        return max;
    }
    let result;
    const lastItem = arr.pop();
    if (height1 === height2) {
        result = Math.max(
            getHeightRec(arr, height1, height2, height2),
            getHeightRec(arr, height1 + lastItem, height2, height2)
        );
    } else {
        result = Math.max(
            getHeightRec(arr, height1, height2, max),
            getHeightRec(arr, height1 + lastItem, height2, max),
            getHeightRec(arr, height1, height2 + lastItem, max)
        );
    }
    arr.push(lastItem);
    return result;
}

function getHeight(arr) {
    return getHeightRec(arr, 0, 0, 0);
}

function treeSum2(tree) {
    const stack = [tree];
    let result = 0;
    while (stack.length) {
        const item = stack.pop();
        if (item) {
            result += item.value;
            stack.push(item.left);
            stack.push(item.right);
        }
    }
    return result;
}

function processDirection(arr, first, end, step) {
    let top = -1;
    for (let i = first; i !== end; i += step) {
        const value = arr[i];
        if (value <= top) {
            arr[i] = -1;
        } else {
            top = value;
        }
        top--;
    }
}

function updateArray(arr) {
    processDirection(arr, 0, arr.length, 1);
    processDirection(arr, arr.length - 1, -1, -1);
    return arr;
}

// --------
updateArray([5, 1, 1, 0, 2, 1, 1, 0]); // [5, -1, -1, -1, 2, -1, 1, -1]

function rec(arr, n, value, result) {
    if (n > 0) {
        for(let i = 0; i < arr.length; ++i) {
            rec(arr, n - 1, value + arr[i], result);
        }
    } else {
        result.push(value);
    }
}

let arr = [1,2,3,4,5]
let r = []
rec(arr, 2, '', r);
console.log(r);