[LeetCode]100、Same Tree

题目描述：

Given two binary trees, write a function to check if they are the same or not.

Two binary trees are considered the same if they are structurally identical and the nodes have the same value.

Example 1:

Input:     1         1
          /        / 
         2   3     2   3

        [1,2,3],   [1,2,3]

Output: true

Example 2:

Input:     1         1
          /           
         2             2

        [1,2],     [1,null,2]

Output: false

Example 3:

Input:     1         1
          /        / 
         2   1     1   2

        [1,2,1],   [1,1,2]

Output: false

思路：

判断两棵二叉树是否相等。结构相等且数值相等。递归方法，从头结点到左子节点再到右子节点。
测试用例的写法：依次给树的根节点、左子节点右子节点赋值即可

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution100 {
    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;
    }
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Solution100 solution100 = new Solution100();
        TreeNode p = new TreeNode(0);
        p.left = new TreeNode(2);
        p.right = new TreeNode(3);
        TreeNode q = new TreeNode(1);
        q.left = new TreeNode(2);
        q.right = new TreeNode(3);
        if(solution100.isSameTree(p, q)){System.out.println("yes");}
        else {
            System.out.println("no");
        }
    }

}