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.

Example 1:

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

Example 2:

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

Example 3:

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

解答

• 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.