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.

思路：

又是树的题目，就用递归的方式来处理。

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) {
        if(p == null && q == null){
            return true;
        }else if(p != null && q == null){
            return false;
        }else if(p == null && q != null){
            return false;
        }else{
            boolean value, left, right;
            //判断值是否相同
            if(p.val == q.val){
                value = true;
            }else{
                value = false;
            }
            //判断左右子树是否分别相同
            left = isSameTree(p.left, q.left);
            right = isSameTree(p.right, q.right);
            //只有值相同，左子树相同，右子树也相同，两棵树才相同
            if(value && left && right){
                return true;
            }else{
                return false;
            }
        }
    }
}