Evaluate Boolean Binary Tree problem from github

solution.ts

/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     val: number
 *     left: TreeNode | null
 *     right: TreeNode | null
 *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.left = (left===undefined ? null : left)
 *         this.right = (right===undefined ? null : right)
 *     }
 * }
 */

const stack: TreeNode[] = [];

function isAtomic(value: number): boolean {
  return value < 2;
}

function evaluateOperation(op: number, left: number, right: number): number {
  if (op == 2) {
    return +(left || right);
  } else if (op == 3) {
    return +(left && right);
  }
  throw new Error();
}

function valueToBoolean(value: number): boolean {
  if (value == 0) return false;
  else if (value == 1) return true;
  throw new Error("");
}

function evaluateTree(root: TreeNode | null): boolean {
  stack.push(root!);
  let result: number = root!.val;

  while (stack.length) {
    const current = stack[stack.length - 1];
    if (isAtomic(current.val)) {
      result = current.val;
      stack.pop();
    } else {
      const left = current.left!;
      const right = current.right!;
      if (isAtomic(left.val) && isAtomic(right.val)) {
        current.val = evaluateOperation(current.val, left.val, right.val);
        result = current.val;
        stack.pop();
      } else if (!isAtomic(left.val)) {
        stack.push(left);
      } else if (!isAtomic(right.val)) {
        stack.push(right);
      }
    }
  }
  return valueToBoolean(result);
}