Given an array nums of positive integers, return the longest possible length of an array prefix of nums, such that it is possible to remove exactly one element from this prefix so that every number that has appeared in it will have the same number of occurrences.
If after removing one element there are no remaining elements, it's still considered that every appeared number has the same number of ocurrences (0).
 
Example 1:
Input: nums = [2,2,1,1,5,3,3,5]
Output: 7
Explanation: For the subarray [2,2,1,1,5,3,3] of length 7, if we remove nums[4]=5, we will get [2,2,1,1,3,3], so that each number will appear exactly twice.

Example 2:
Input: nums = [1,1,1,2,2,2,3,3,3,4,4,4,5]
Output: 13

Example 3:
Input: nums = [1,1,1,2,2,2]
Output: 5

Example 4:
Input: nums = [10,2,8,9,3,8,1,5,2,3,7,6]
Output: 8

 
Constraints:

2 <= nums.length <= 10^5
1 <= nums[i] <= 10^5

```python

USER_FILENAME = "<user_code>"
import sys, json, builtins
import math, heapq, bisect, itertools, functools, collections, statistics, fractions, decimal, operator, array, random, re, string, os, pathlib
try:
    import resource as _res
except Exception:
    _res = None
from collections import Counter, defaultdict, deque, OrderedDict
from functools import lru_cache, reduce
from itertools import accumulate, permutations, combinations, product
from math import gcd, ceil, floor, sqrt
from decimal import Decimal
try:
    from typing import *
except Exception:
    pass
try:
    sys.setrecursionlimit(1_000_000)
except Exception:
    pass
try:
    import site as _site
    try:
        _sys_sites = _site.getsitepackages() if hasattr(_site, "getsitepackages") else []
        for _p in _sys_sites:
            if _p and _p not in sys.path:
                sys.path.append(_p)
    except Exception:
        pass
    try:
        _usp = _site.getusersitepackages()
        if isinstance(_usp, str):
            _usp = [_usp]
        for _p in _usp:
            if _p and _p not in sys.path:
                sys.path.append(_p)
    except Exception:
        pass
except Exception:
    pass

def _disabled_input(*args, **kwargs):
    raise RuntimeError("input() is disabled in callable mode")
builtins.input = _disabled_input

ns = {"__name__": "__judge__"}  # prevent if __name__ == "__main__" blocks
for _k, _v in list(globals().items()):
    if not _k.startswith("_"):
        ns[_k] = _v
_CODE = 'class Solution:\n    def isvalid(self,D):\n        if len(D)==1:\n            a = min(D)\n            if a==1 or D[a]==1:\n                # a==1: all lengths are unitary (like [1,2,3,4,...]), so removing anything is fine\n                # D[a]==1, we have a unique length occurence (like [4,4,4,4,...]), so...\n                #          so we can pop one element and be fine\n                return True\n            return False\n        # len(D)==2 now\n        a,b = min(D),max(D)\n        if a==D[a]==1: \n            # If we remove from a chain of length \\"a\\", we will create something smaller than \\"b\\", so...\n            # The only way to be fine is to have a single element, like [1,2,2,2,3,3,3,...]\n            #     - If we have more of the smallest length, we\'re into trouble\n            return True\n        # Remove from \\"b\\"\n        return True if ( D[b]==1 and (a+1)==b ) else False\n    def maxEqualFreq(self, A):\n        best = 0\n        B = Counter() # Count number of repetitions/length (per value)\n        C = Counter() # Count number of times a length has been seen\n        for i,x in enumerate(A):\n            old = B[x]\n            if old:\n                if C[old]==1:\n                    C.pop(old)\n                else:\n                    C[old] -= 1\n            B[x]     += 1 # increase rep. counter\n            C[old+1] += 1 # Register new length seen\n            #\n            if len(C)<3 and self.isvalid(C):\n                best = i+1\n        return best'
_co = compile(_CODE, USER_FILENAME, "exec")
exec(_co, ns, ns)

_target = None
_fn_name = 'maxEqualFreq'
if _fn_name:
    if "Solution" in ns:
        try:
            _obj = ns["Solution"]()
            if hasattr(_obj, _fn_name):
                _target = getattr(_obj, _fn_name)
        except Exception:
            _target = None
    if _target is None and _fn_name in ns and callable(ns[_fn_name]):
        _target = ns[_fn_name]
# Fallback: if there's exactly one user-defined function, use it
if _target is None:
    _cands = [v for k, v in ns.items() if callable(v) and getattr(v, "__module__", "") in ("__judge__", "__main__")]
    _user_funcs = [c for c in _cands if getattr(c, "__name__", "").startswith("_") is False]
    if len(_user_funcs) == 1:
        _target = _user_funcs[0]
if _target is None:
    raise RuntimeError(f"Could not resolve callable '{_fn_name}'")

_raw = sys.stdin.read().strip()
if _raw:
    _parsed = json.loads(_raw)
    if isinstance(_parsed, dict):
        _kwargs = _parsed.get("kwargs", {})
        _args = _parsed.get("args", [])
    else:
        _args, _kwargs = _parsed, {}
else:
    _args, _kwargs = [], {}
if not isinstance(_args, (list, tuple)):
    _args = [_args]
_res = _target(*_args, **_kwargs)
try:
    sys.stdout.write(repr(_res) + "\n")
except Exception:
    pass

```

Measured memory_bytes: 7862