Approach
Depth-first search
For ABC397 E — Path Decomposition of a Tree, the implementation follows one branch at a time, making it suitable for components, trees, backtracking, or dependency exploration.
- Define the state carried into one recursive or stack frame.
- Mark or choose the current state before exploring children.
- Combine child results or undo the choice when the branch finishes.
Code notes
- 59 lines of Python from the credited upstream file abc397_e.py.
- The implementation visibly relies on sequence storage, ordered lookup.
- No explicit loop blocks detected, together with recursive traversal.
Complexity
Count unique states for graph traversal; for backtracking, count the branching factor and maximum depth.
Check the problem constraints before deciding whether this complexity will pass.
Use this to learn the idea, then write your own version.
12 3ok = True4 5 6def main():7 import sys8 9 sys.setrecursionlimit(10**8)10 11 input = sys.stdin.readline12 13 n, k = map(int, input().split())14 nk = n * k15 graph = [[] for _ in range(nk)]16 17 for _ in range(nk - 1):18 ai, bi = map(int, input().split())19 ai -= 120 bi -= 121 22 graph[ai].append(bi)23 graph[bi].append(ai)24 25 def dfs(cur, parent=-1):26 global ok27 28 size_total = 129 degree = 030 31 for child in graph[cur]:32 if child == parent:33 continue34 35 size = dfs(child, cur)36 37 if size % k != 0:38 degree += 139 40 size_total += size41 42 if size_total % k != 0:43 degree += 144 if degree >= 3:45 ok = False46 47 return size_total48 49 dfs(0)50 51 if ok:52 print("Yes")53 else:54 print("No")55 56 57if __name__ == "__main__":58 main()59