Cover "Manhattan skyline" using the minimum number of rectangles in JavaScript

Codility Stonewall Solution Using JavaScript Stack

// ===== ANSWER

function solution(H) {
    // write your code in JavaScript (Node.js 8.9.4)
    let stack = [];
    let count = 0;
    let height = 0;
    
    // adds a block to the stack when value exceeds current height
    const addBlock = (value) => {
        if (value > height) {
            stack.push(value - height);
            height = value;
            count += 1;
        }
    }
    
    // adjust the blocks when value is lower than current height
    const popDown = (value) => {
        while (value < height) { // adjust to nearest block height
            height -= stack.pop();
        }  
        if (value > height) {
            addBlock(value)
        }
    }
    // loop through the set and make adjustments
    for (let i = 0; i < H.length; i += 1) {
        let value = H[i];
        if (value < height) {
            popDown(value)
        } else if (value > height) { // ignore value equal to height
            addBlock(value)
        }
    }
    
    return count
}

// ===== PROBLEM
https://app.codility.com/demo/results/trainingE6TPQZ-NMX/
-  See detailed problem below

// ===== Task description
You are going to build a stone wall. The wall should be straight and N meters long, and its thickness should be constant; however, it should have different heights in different places. The height of the wall is specified by an array H of N positive integers. H[I] is the height of the wall from I to I+1 meters to the right of its left end. In particular, H[0] is the height of the wall's left end and H[N−1] is the height of the wall's right end.

The wall should be built of cuboid stone blocks (that is, all sides of such blocks are rectangular). Your task is to compute the minimum number of blocks needed to build the wall.

Write a function:

function solution(H);

that, given an array H of N positive integers specifying the height of the wall, returns the minimum number of blocks needed to build it.

For example, given array H containing N = 9 integers:

  H[0] = 8    H[1] = 8    H[2] = 5
  H[3] = 7    H[4] = 9    H[5] = 8
  H[6] = 7    H[7] = 4    H[8] = 8
the function should return 7. The figure shows one possible arrangement of seven blocks. 

===== Assume that:

N is an integer within the range [1..100,000];
each element of array H is an integer within the range [1..1,000,000,000].
Complexity:

expected worst-case time complexity is O(N);
expected worst-case space complexity is O(N) (not counting the storage required for input arguments).