Short and clear JavaScript solution building left, bottom, then right

  • 0
    var boundaryOfBinaryTree = function(root) {
        if (!root) return [];
        if (!root.left && !root.right) return [root.val];
        const res = [root.val];
        buildSide(root.left, 'left', res);
        buildBottom(root, res);
        const right = [];
        buildSide(root.right, 'right', right);
        return [...res, ...right.reverse()];
    function buildSide(root, side, res) {
        if (!root) return;
        if (root.left || root.right) res.push(root.val);
        if (root[side]) buildSide(root[side], side, res);
        else buildSide(root[side === 'left' ? 'right' : 'left'], side, res);
    function buildBottom(root, res) {
        if (!root) return;
        if (!root.left && !root.right) res.push(root.val);
        buildBottom(root.left, res);
        buildBottom(root.right, res);

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