# 100. Same Tree

### Leetcode

<https://leetcode.com/problems/same-tree/>

### 題目

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.

&#x20;

**Example 1:**

![](https://assets.leetcode.com/uploads/2020/12/20/ex1.jpg)

```
Input: p = [1,2,3], q = [1,2,3]
Output: true
```

**Example 2:**

![](https://assets.leetcode.com/uploads/2020/12/20/ex2.jpg)

```
Input: p = [1,2], q = [1,null,2]
Output: false
```

**Example 3:**

![](https://assets.leetcode.com/uploads/2020/12/20/ex3.jpg)

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

### 解答 <a href="#ti-jie" id="ti-jie"></a>

* **方法一**

Recursion

```
var isSameTree = function(p, q) {
    if (!p && !q) return true;
    if (p?.val !== q?.val) return false;
    
    return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
};
```

Runtime: 56 ms, faster than 97.72% of JavaScript online submissions for Same Tree.

Memory Usage: 42.8 MB, less than 5.16% of JavaScript online submissions for Same Tree.

* **方法二**

Iteration

```
var isSameTree = function(p, q) {
    const isEqual = (p, q) => {
        if (!p && !q) return true;
        // 可能其中一個不存在 -> return false
        if (p?.val === q?.val) return true;
        return false;
    }
        
    const queue = [[p, q]];
    while(queue.length) {
        const pair = queue.shift();
        const node1 = pair[0];
        const node2 = pair[1];
        
        if (!isEqual(node1, node2)) return false;
        // 如果 node1 不存在，node2 存在的話，上一行就直接 return false 了
        if (node1) {
            queue.push([node1.left, node2.left]);
            queue.push([node1.right, node2.right]);
        }
    }

    return true;
};
```

Runtime: 100 ms, faster than 30.94% of JavaScript online submissions for Same Tree.

Memory Usage: 42.5 MB, less than 34.35% of JavaScript online submissions for Same Tree.
