1
var subtreeWithAllDeepest = function (root) {
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  // keep track of deepest till now
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  // if left right has both deepest than it will be the ans;
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  let mx = 0,
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    rm = 0,
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    ans = null;
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  const compute = (r = root, d = 0) => {
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    if (!r) {
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      rm = Math.max(rm, d);
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      return d;
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    }
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    const ld = compute(r.left, d + 1);
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    const rd = compute(r.right, d + 1);
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    if (ld == rd && ld == mx) {
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      ans = r;
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    }
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    if (mx < rm) {
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      ans = r;
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      mx = rm;
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    }
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    return Math.max(ld, rd);
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  };
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  compute();
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  return ans;
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};