Algorithm

100.same-tree

Description:

Given the roots of two binary trees p and q, write a function to check if they are the same or not.

Two binary trees are considered the same if they are structurally identical, and the nodes have the same value.

Example:

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Input: p = [1,2,3], q = [1,2,3]
   1        1
  / \      / \
 2   3    2   3

Output: true
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Input: p = [1,2], q = [1,null,2]
   1        1
  /          \
 2            2

Output: false
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Input: p = [1,2,1], q = [1,1,2]
   1        1
  / \      / \
 2   1    1   2

Output: false

First Answer (Recursive):

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<?php

namespace LeetCode\SameTree;

/**
 * Definition for a binary tree node.
 * class TreeNode {
 *     public $val = null;
 *     public $left = null;
 *     public $right = null;
 *     function __construct($val = 0, $left = null, $right = null) {
 *         $this->val = $val;
 *         $this->left = $left;
 *         $this->right = $right;
 *     }
 * }
 */
class Solution
{
    /**
     * @var bool $answer
     */
    protected $answer = true;
    /**
     * @param TreeNode $p
     * @param TreeNode $q
     * @return bool
     */
    public function isSameTree($p, $q)
    {
        $this->findAnswer($p, $q);
        return $this->answer;
    }

    /**
     * @param TreeNode $p
     * @param TreeNode $q
     */
    private function findAnswer($p, $q)
    {
        if ($p->val !== $q->val) {
            return $this->answer = false;
        }

        if (($p->left->val !== $q->left->val) || ($p->right->val !== $q->right->val)) {
            return $this->answer = false;
        }

        if (!is_null($p->left) && !is_null($q->left)) {
            $this->findAnswer($p->left, $q->left);
        }

        if (!is_null($p->right) && !is_null($q->right)) {
            $this->findAnswer($p->right, $q->right);
        }
    }
}
  • Time Complexity: O(n)

ʕ •ᴥ•ʔ：很久沒寫文了，最近覺得情況不算太好。
重新努力，用寫文把狀態找回來。