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 (Java)

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    private boolean trav(TreeNode n, TreeNode m) {
        if (n != null && m != null) {
            if (n.val != m.val) {
                return false;
            }
            return (trav(n.left, m.left) && trav(n.right, m.right));
        } else {
            return n == null && m == null;
        }
    }

    public boolean isSameTree(TreeNode p, TreeNode q) {
        if (p == null && q == null) {
            return true;
        } else if (p == null || q == null) {
            return false;
        }
        return trav(p, q);
    }
}

Solution 1 (Javascript)

/**
 * 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 (Javascript)

/**
 * 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).