[Leetcode]100. Same Tree -David_Lin

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.

思路：同时递归两棵树，如果节点值不相等或者一棵树已经递归到头了而另一棵还没有，返回false;

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
        if (p==null&&q==null)
            return true;                 //一开始如果传进两颗空树，返回true
        if ((p==null&&q!=null)||(p!=null&&q==null))
            return false;                //递归过程中，一棵树递归到头了，而另一颗没有
        if (p.val!=q.val)
            return false;
        return isSameTree(p.left,q.left)&&isSameTree(p.right,q.right); 
                                              // 同时递归
    }
}