java递归解决

先写一个方法，传入两棵根节点值相同的树，判断tree1是否和tree2结构一样

public boolean doesTree1HasTree2(TreeNode tree1, TreeNode tree2){
     if ( tree2 == null ){
         return true;
     }
     if ( tree1 == null ){
         return false;
     }

     if ( tree1.val != tree2.val ){
         return false;
     }
     return doesTree1HasTree2(tree1.left, tree2.left) && doesTree1HasTree2(tree1.right, tree2.right);
 }

再写一个方法来遍历大树，找到一个和小树根节点值相等的节点，以该节点和小树根节点的值为参数调用上面的方法即可

public  boolean HasSubtree(TreeNode root1, TreeNode root2) {
     if ( root2 == null || root1 == null){
         return false;
     }
     return doesTree1HasTree2(root1, root2) || HasSubtree(root1.left, root2) || HasSubtree(root1.right, root2);
 }