from collections import defaultdict import sys sys.setrecursionlimit(10**6) def solve(N, M, edges): longest = {} def get_longest(start): if start in longest: return longest[start] next_edges = edges.get(start) if not next_edges: ret = 0 else: ret = max(get_longest(v) for v in edges[start]) + 1 longest[start] = ret return ret return max(get_longest(v) for v in edges) def main(): N, M = map(int, input().split()) edges = defaultdict(set) for i in range(M): v1, v2 = map(int, input().split()) edges[v1].add(v2) print(solve(N, M, edges)) main()

def solve(N, M, edges): longest = [-1] * (N + 1) for i in range(N + 1): if not edges[i]: longest[i] = 0 def get_longest(start): ret = longest[start] if ret != -1: return ret next_edges = edges.get(start) if not next_edges: ret = 0 else: ret = max(get_longest(v) for v in edges[start]) + 1 longest[start] = ret return ret return max(get_longest(v) for v in edges)

cdef get_longest(long start, dict edges, long[:] longest): if longest[start] != -1: return longest[start] cdef list next_edges next_edges = edges.get(start) if not next_edges: ret = 0 else: #ret = max(get_longest(v, edges, longest) for v in edges[start]) + 1 ret = 0 for v in edges[start]: x = get_longest(v, edges, longest) + 1 if x > ret: ret = x longest[start] = ret return ret def solve(N, M, edges): cdef array.array longest = pyarray.array('l', [-1] * (N + 1)) return max(get_longest(v, edges, longest) for v in edges)

def solve(N, M, edges): longest = {} stack = [v for v in edges] while stack: v = stack.pop() if v > 0: if v in longest: continue next_edges = edges.get(v) stack.append(-v) if next_edges: stack.extend(next_edges) else: next_edges = edges.get(-v) if not next_edges: ret = 0 else: ret = max(longest[x] for x in next_edges) + 1 longest[-v] = ret return max(longest[v] for v in edges)