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 (root1 == null || root2 == null)    return false;
        if (isSameSubStructure(root1, root2))    return true; // 结构对等的比较
        return HasSubtree(root1.left, root2) || HasSubtree(root1.right, root2); // 子树中查找对等结构
    }
    private boolean isSameSubStructure(TreeNode root1,TreeNode root2) {
        if (root2 == null)    return true; // B的子结点为空就不用判断了
        if (root1 == null)    return false;
        return root1.val == root2.val && isSameSubStructure(root1.left, root2.left)
            && isSameSubStructure(root1.right, root2.right);
    }
}