same-tree/symmetric-tree

题目一：same-tree
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.

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {    public:    bool isSameTree(TreeNode *p, TreeNode *q) {        if(!p && !q)            return true;        if(p && !q)            return false;        if(!p && q)            return false;        if(p->val ==q->val)            return isSameTree(p->left,q->left) && isSameTree(p->right,q->right);        else            return false;    }};

题目二：symmetric-tree
Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).
For example, this binary tree is symmetric:
1
/ \
2 2
/ \ / \
3 4 4 3

But the following is not:
1
/ \
2 2
\ \
3 3

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {    public:    bool isSymmetric(TreeNode *root) {        if(root==NULL)            return true;        return ismirror(root->left,root->right);    }    bool ismirror(TreeNode *p,TreeNode *q)    {        if(!p && !q)            return true;        if(!p && q)            return false;        if(p && !q)            return false;        if(p->val ==q->val)            return ismirror(p->left,q->right) && ismirror(p->right,q->left);        else            return false;    }};