class Solution {
    public boolean isSubStructure(TreeNode A, TreeNode B) {
        if(B == null || A == null) return false;
        if(isContain(A, B)) return true;
        return isSubStructure(A.left, B) || isSubStructure(A.right, B);
    }

    boolean isContain(TreeNode A, TreeNode B){
        if(B == null) return true;
        if(A == null) return false;
        if(A.val != B.val) return false;
        return isContain(A.left, B.left) && isContain(A.right, B.right);
    }
}