100.Same-Tree

100. Same Tree

题目地址

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

题目描述

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

代码

Approach #1 Recursion

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
  public boolean isSameTree(TreeNode p, TreeNode q) {
        if (p == null && q == null)    return true;
    if (p == null || q == null)    return false;
    if (p.val != q.val)    return false;

    return isSameTree(p.right, q.right)
                  && isSameTree(p.left, q.left);
  }
}

Approach #2 Iteration

class Solution {
  public boolean isSameTree(TreeNode p, TreeNode q) {
      if (!check(p, q)) return false;

    ArrayDeque<TreeNode> deqP = new ArrayDeque<TreeNode>();
    ArrayDeque<TreeNode> deqQ = new ArrayDeque<TreeNode>();
    degP.addLast(p);
    degQ.addLast(q);

    while (!deqP.isEmpty()) {
      p = deqP.removeFirst();
      q = deqQ.removeFirst();

      if (!check(p, q))        return false;
      if (p != null) {
        if (!check(p.left, q.left))    return false;
        if (p.left != null) {
          deqP.addLast(p.left);
          deQ.addLast(q.left);
        }

        if (!check(p.right, q.right))    return false;
        if (p.right != null) {
          deqP.addLast(p.right);
          deQ.addLast(q.right);
        }
      }
    }
    return true;
  }

  public boolean check(TreeNode p, TreeNode q) {
    if (p == null && q == null)        return true;
    if (p == null || q == null)        return false;
    if (p.val != q.val)    return false;

    return true;
  }

}