Path

let path (g : int array array) =
    let n = Array.length g in
    let ans_arr = Array.make n 1
    and answer = ref 0 in
        for i = 0 to (n - 1) do
            let cur = g.(i) in
            let cur_size = Array.length cur in
            answer := max !answer (ans_arr.(i));
            for j = 0 to (cur_size - 1) do
                if cur.(j) > (i + 1) then
                    ans_arr.(cur.(j) - 1) <- max (ans_arr.(cur.(j) - 1) + 1) (ans_arr.(i) + 1)
            done;
        done;
    !answer;

(*path [| [|3;5;6|]; [|4|]; [|6|]; [|5|]; [|6|]; [|1|] |] = 4;;*)

type node = {value: int; mutable neighbours: int list}

type graph = node array

let g_make n =
    Array.init n (fun i -> {value = i; neighbours = []})

let neighbours g i =
    g.(i).neighbours

let size g =
    Array.length g

let insert_edge g i j =
    g.(i).neighbours <- j :: g.(i).neighbours;
    g.(j).neighbours <- i :: g.(j).neighbours

let path2 g =
    let n = size g in
    let ans_arr = Array.make n 1
    and answer = ref 0 in
        for i = 0 to (n - 1) do
            let cur = Array.of_list (neighbours g i) in
            let cur_size = Array.length cur in
            answer := max !answer (ans_arr.(i));
            for j = 0 to (cur_size - 1) do
                if cur.(j) > (i + 1) then
                    ans_arr.(cur.(j) - 1) <- max (ans_arr.(cur.(j) - 1) + 1) (ans_arr.(i) + 1)
            done;
        done;
    !answer;;


let test = g_make 6;;
insert_edge test 0 2;
insert_edge test 0 4;
insert_edge test 0 5;
insert_edge test 1 3;
insert_edge test 2 5;
insert_edge test 3 4;
insert_edge test 4 5;
path2 test;