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.

题目含义：判断两个二进制树结构是否相等

1     public boolean sameTree(TreeNode p, TreeNode q) 2     { 3         if (p==null && q==null) return true; 4         if (p==null || q==null) return false; 5         if (p.val != q.val) return false; 6         return sameTree(p.left,q.left) && sameTree(p.right,q.right); 7     }  8     public boolean isSameTree(TreeNode p, TreeNode q) { 9         return sameTree(p,q);        10     }