[LeetCode]: 100: Same Tree

题目：

Given two binary trees, write a function to check if they are equal or not.

Two binary trees are considered equal if they are structurally identical and the nodes have the same value.

解析：

比较两个二叉树是否相同采用将二叉树进行“先序遍历”，“中序遍历”和“后序遍历”，如果其中有两种遍历的结果相同，则这两个二叉树相等

代码：

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
public class Solution {

public boolean isSameTree(TreeNode p, TreeNode q) {

String ResultL1 = Front(p);
String ResultL2 = Front(q);

String ResultL3 = Middle(p);
String ResultL4 = Middle(q);
/*
String ResultL5 = Last(p);
String ResultL6 = Last(q);
*/

if(ResultL1.equals(ResultL2) && ResultL3.equals(ResultL4)){
return true;
}
else{
return false;
}
}

public static String Front(TreeNode Tree){
if(Tree == null){
return "X";
}

String strResult  = "";

strResult += Tree.val;
strResult += Front(Tree.left);
strResult += Front(Tree.right);

return strResult;
}

public static String Middle(TreeNode Tree){
if(Tree == null){
return "X";
}

String strResult  = "";
strResult += Middle(Tree.left);
strResult += Tree.val;
strResult += Middle(Tree.right);

return strResult;
}

public static String Last(TreeNode Tree){
if(Tree == null){
return "X";
}

String strResult  = "";
strResult += Last(Tree.left);
strResult += Last(Tree.right);
strResult += Tree.val;

return strResult;
}

}

网上高人的代码如下：添加了空树的判断

bool isSameTree(TreeNode *p, TreeNode *q) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
if (p == NULL && q == NULL)
return true;
else if (p == NULL || q == NULL)
return false;
return p->val == q->val && isSameTree(p->left, q->left)
&& isSameTree(p->right, q->right);
}