[LeetCode]100. Same Tree

题目描述：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.
分析：判断两个二叉树是否相等

解题思路:递归判断两颗子树是否相等。判断条件:都为叶子结点返回true；其中一个节点存在，另一个节点不存在返回false；两个节点都存在，且相等，递归该节点的左子树和右子树，不想等则返回false。

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);        }else{            return false;        }    }