题解与来源题共享。已有题解默认通过；新增或编辑后需由来源域管理员审核。待审核、驳回题解仅作者和审核管理员可见。来源域：system

• 0

  li1005345206 LV 6 @ 2026-5-11 16:36:00

  import os
  import sys
  n = int(input())
  a = map(int, input().split())
  s = [0]
  for i in a:
      s.append(s[-1] + i)
  t = s[-1] // 3
  if t * 3 != s[-1]:
      print(0)
  else:
      c0 = 0
      c1 = 0
      ind = []
      for i0 in range(1, len(s)):
          i = s[i0]
          if i == t:
              c0 += 1
              ind.append(i0)
          elif i == s[-1] - t:
              c1 += 1
      if t != 0:
          print(c0 * c1)
      else:
          r = 0
          for i in range(len(ind)):
              for j in range(i + 1, len(ind)):
                  if ind[j] == n:
                      continue
                  r += 1
              
          print(r)