输入两棵二叉树A，B，判断B是不是A的子结构。（ps：我们约定空树不是任意一个树的子结构）
/**
public class TreeNode {
int val = 0;
TreeNode left = null;
TreeNode right = null;
public TreeNode(int val) {
this.val = val;
}
}
*/
public class Solution{
public boolean HasSubtree(TreeNode root1,TreeNode root2) {
if(root2==null) return false;
if(root1==null && root2!=null) return false;
boolean flag = false;
flag = isSubTree(root1,root2);
if(!flag){
flag = HasSubtree(root1.left, root2);
if(!flag){
flag = HasSubtree(root1.right, root2);
}
}
return flag;
}
private boolean isSubTree(TreeNode root1, TreeNode root2) {
if(root2==null) return true;
if(root1==null && root2!=null) return false;
if(root1.val==root2.val){
return isSubTree(root1.left, root2.left) && isSubTree(root1.right, root2.right);
}else{
return false;
}
}
}
