cf补题:

https://codeforces.com/contest/1490/problem/B

审题不清，必须保证每一步都是increasing

官方题解:

https://codeforces.com/blog/entry/87874

ac代码

#pragma GCC optimize(2)
#pragma GCC optimize(3)
#include <bits/stdc++.h>
using namespace std;
#define IO std::ios::sync_with_stdio(false); cin.tie(0)
#define ll long long
#define ull unsigned long long
#define SZ(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define rep(i, l, r) for (int i = l; i <= r; ++i)
#define per(i, l, r) for (int i = l; i >= r; --i)
#define mset(s, _) memset(s, _, sizeof(s))
#define mcpy(s, _) memcpy(s, _, sizeof(s))
#define pb push_back
#define pii pair <int, int> 
#define vi vector<int>
#define vpii vector<pii> 
#define mp(a, b) make_pair(a, b)
#define debug system("pause")
#define pll pair <ll, ll>
#define fir first
#define sec second
#define inf 0x3f3f3f3f
#define pline cout << endl << endl 
inline int lowbit(int x) {return x & -x;} 
inline bool cmp(int a, int b) {return a > b;}
template< typename T > inline void get_min(T &x, T y) {if(y < x) x = y;}
template< typename T > inline void get_max(T &x, T y) {if(x < y) x = y;}
inline int read() {
  int x = 0, f = 0; char ch = getchar();
  while (!isdigit(ch)) f |= ch == '-', ch = getchar();
  while (isdigit(ch)) x = 10 * x + ch - '0', ch = getchar();
  return f ? -x : x;
}
template<typename T> inline void print(T x) {
  if (x < 0) putchar('-'), x = -x;
  if (x >= 10) print(x / 10);
  putchar(x % 10 + '0');
}
template<typename T> inline void print(T x, char let) {
  print(x), putchar(let);
}

const int N = 3e4 + 10;
int t, n;
int a[N];
int num[N];
int cnt;
int ans;
map<int, int> mp;
int main(){
    IO;
    cin >> t;
    while(t -- ) {
        cnt = 0, ans = 0;
        mset(num, 0);
        cin >> n;
        rep(i, 0, n - 1) {
            cin >> a[i];
            int t = a[i] % 3; 
            num[t] ++ ;
//          cout << a[i] << " " << t << endl;
        }

//      rep(i, 0, 2) cout << i << " " << num[i] << endl;

        int x = n / 3;

        int id;
        rep(i, 0, 2) {
            if(num[i] < x) cnt ++ , id = i;
        }

        if(cnt == 1) {
            rep(i, 0, 2) {
                if(i != id) {
                    if(i < id) ans += abs(i - id) * abs(num[i] - x);
                    else ans += abs(3 - i + id) * abs(num[i] - x);
//                  cout << "***" << endl;
                }
            }
            cout << ans << endl;
            continue;   
        } 

        ans = 0;
        cnt = 0;
        id = 0;
        rep(i, 0, 2) {
            if(num[i] > x) cnt ++ , id = i;
        }

        if(cnt == 1) {
            rep(i, 0, 2) {
                if(i != id) {
                    if(i > id) ans += abs(i - id) * abs(x - num[i]);
                    else ans += abs(3 - id + i) * abs(x - num[i]);
                }
//              cout << "!!!!" << endl;
            }
            cout << ans << endl;
            continue;
        }   

        cout << 0 << endl;
    }

    return 0;
}

还是太菜了，debug把我血压拉满了QwQ