LeetCode-Same Tree

和上一题几乎一模一样，只是不用左右交替了，更简单，把上个symmetric的helper function稍微改一下就是这个题了

public class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
        if ( p == null || q == null ){
            return p==q;
        }
        return (p.val == q.val) && isSameTree(p.left,q.left) && isSameTree(p.right,q.right);
    }
}