《剑指Offer》题目：树的子结构

class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;
    }

}
public class HasSubtree {
    public boolean hasSubtree(TreeNode root1,TreeNode root2) {
        boolean res = false;
        if (root1 != null && root2 !=null){
            if (root1.val == root2.val){
                //这时候判断两个二叉树是否有相同的结构
                res = isAHasB(root1, root2);
            }
            if (!res){
                res = hasSubtree(root1.left,root2);
            }
            if (!res){
                res = hasSubtree(root1.right, root2);
            }
        }
        return res;
    }
　　　//判断两个二叉树是否有相同的结构
    public boolean isAHasB(TreeNode root1,TreeNode root2){
        if (root2 == null) return true;
        if (root1 == null) return false;
        if (root1.val != root2.val) return false;

        return isAHasB(root1.left, root2.left) && isAHasB(root1.right, root2.right);
    }

}