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| 1 | +/** |
| 2 | + * Definition for a binary tree node. |
| 3 | + * class TreeNode { |
| 4 | + * public $val = null; |
| 5 | + * public $left = null; |
| 6 | + * public $right = null; |
| 7 | + * function __construct($value) { $this->val = $value; } |
| 8 | + * } |
| 9 | + */ |
| 10 | +class Solution { |
| 11 | + |
| 12 | + /** |
| 13 | + * @param TreeNode $root |
| 14 | + * @return Integer[][] |
| 15 | + */ |
| 16 | + function levelOrderBottom($root) { |
| 17 | + $result = []; |
| 18 | + // Hit the end, return an empty list directly |
| 19 | + if ($root == null) { |
| 20 | + return $result; |
| 21 | + } |
| 22 | + |
| 23 | + $self = []; |
| 24 | + array_push($self, $root->val); |
| 25 | + |
| 26 | + $left = self::levelOrderBottom($root->left); |
| 27 | + $right = self::levelOrderBottom($root->right); |
| 28 | + |
| 29 | + // Return directly on leaf will cause the depth of left/right tree are not the same |
| 30 | + // need to merge the lists based on different index. |
| 31 | + $startIdx = abs(count($left) - count($right)); |
| 32 | + if (count($left) >= count($right)) { |
| 33 | + for ($i = $startIdx, $j = 0; $j < count($right); $j++) { |
| 34 | + array_push($left[$i + $j], ...$right[$j]); |
| 35 | + } |
| 36 | + array_push($left, $self); |
| 37 | + return $left; |
| 38 | + } else { |
| 39 | + for ($i = $startIdx, $j = 0; $j < count($left); $j++) { |
| 40 | + array_splice($right[$i + $j], 0, 0, $left[$j]); |
| 41 | + } |
| 42 | + array_push($right, $self); |
| 43 | + return $right; |
| 44 | + } |
| 45 | + } |
| 46 | +} |
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