LeetCode 100. Same Tree

题意：给你两个二叉树，然后判定两棵树是否完全相等。

大意：用递归，先判定两个根的val值是否相等，不等就return false，相等就判定两棵树的左子树和右子树是否相等。

/**
 * 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) {
            if(p != null) return false;
            if(q != null) return false;
            return true;
        }
        
        if(p.val != q.val) return false;
        else {
            boolean leftIsSame = isSameTree(p.left, q.left);
            boolean rightIsSame = isSameTree(p.right, q.right);
            
            if(leftIsSame && rightIsSame) return true;
            else return false;
        }
    }
}