consider the following two graphs. I want to calculate the symmetry factors for them . I am using field contraction method for that. but I am getting 2 for the 2 vertex diagram and 1 for the zero vertex diagram where it should be 4 and two respectively. Can anyone do it for me. I am writing briefly the reason behind my findings. i am considering $$\phi^3$$ theory. So for vertex zero case i don't have any factors left. In case of two vertex case. say I am denoting two vertices as v and w and the sources as x and y. ok. now x can be combined with 6 possible ways and therefore y can be combined with 2 possible ways. now if i call that one v. then i am left with one field in v and 3 in w. they can combine 3 ways. so i got 6*3*2. now i have to divide it by 2*(3!*3!). and this would give me 1/2. so the symmetry factor is two. but that is a wrong answer. so where did i missed the point.??