100. Same Tree

Problem

Given two binary trees, 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:     1         1
          / \       / \
         2   3     2   3

        [1,2,3],   [1,2,3]

Output: true

Example 2:

Input:     1         1
          /           \
         2             2

        [1,2],     [1,null,2]

Output: false

Example 3:

Input:     1         1
          / \       / \
         2   1     1   2

        [1,2,1],   [1,1,2]

Output: false

Solution 1

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} p
 * @param {TreeNode} q
 * @return {boolean}
 */
var isSameTree = function(p, q) {
  if ((!p && q) || (p && !q) || (p && q && p.val !== q.val)) return false;
  if (p && q) return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
  return true;
};

Explain:

nope.

Complexity:

• Time complexity : O(n). n 为节点数。
• Space complexity : O(1).

Solution 2

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} p
 * @param {TreeNode} q
 * @return {boolean}
 */
var isSameTree = function(p, q) {
  var s1 = [p];
  var s2 = [q];
  var ll = null;
  var rr = null;

  while (s1.length && s2.length) {
    ll = s1.pop();
    rr = s2.pop();

    if (!ll && !rr) continue;
    if (!ll || !rr) return false;
    if (ll.val !== rr.val) return false;

    s1.push(ll.left);
    s1.push(ll.right);
    s2.push(rr.left);
    s2.push(rr.right);
  }

  return true;
};

Explain:

nope.

Complexity:

• Time complexity : O(n). n 为节点数。
• Space complexity : O(n).