100. Same Tree

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.

判断两个树是否完全相同，判断的标准是每个节点的值是否相等，若相等的话，其左右节点是否相同，然后用递归调用这个函数，对节点的左子树和右子树继续判断即可，（首先判断一下两颗树是否都为空），代码如下：

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);
        }
        return false;