100. Same Tree（五星）
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.
給出兩個二叉樹，寫一個算法來檢查它們是否相同。若兩棵樹結構完全相同，且每個節點有相同值，則為兩棵樹相同。
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
大神答案micheal.zhou
遞歸方式，簡單明了~
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 isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
return false;
} 我自己的答案（非遞歸），這個題其實主要考察二叉樹的遍歷，下面鏈接裏非常詳細地總結了二叉樹前、中、後序遍歷的遞歸和非遞歸方法，可讀性比較高。
http://blog.csdn.net/apandi_/article/details/52916523
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
import java.util.Stack;
class Solution {
public boolean isSameTree(TreeNode p, TreeNode q) {
Stack<TreeNode> st_p = new Stack<TreeNode>();
Stack<TreeNode> st_q = new Stack<TreeNode>();
while (p != null || !st_p.empty()) {
while (p != null) {
if (q == null)
return false;
if (p.val != q.val)
return false;
st_p.push(p);
st_q.push(q);
p = p.left;
q = q.left;
}
if (!st_p.empty()) {
if(st_q.empty()||q!=null)
return false;
p=st_p.pop();
q=st_q.pop();
p=p.right;
q=q.right;
}
}
if (q!=null||!st_q.empty())
return false;
return true;
}
}
100. Same Tree（五星）