[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);  
    }