题目链接：CF 或者 洛谷
对于绝对值的几何意义来说，这题是在直线上的两点间的距离，为了总的距离和最下，首先最好让它们两两之间最好都紧挨着。
由于询问的是 \((i,j)\) 不重不漏的对有关，即 \((i<j)\ +\ (i>j)\ +\ (i=j)=all(i,j)\)，又因为，\((i,j)\) 的贡献和 \((j,i)\) 相同且重复，所以我们只需要加一个偏序关系就行了。
考虑一下题目让求的东西：
\[\min{\sum_{i=1}^{k}\sum_{j=1}^{i-1} \left | x_i -x_j \right |} \]先考虑去绝对值。其实只需要让 \(x\) 排序就行，因为 \(j<i\)，所以 \(x_i\ge x_j\)，绝对值就就能去掉了。
\[\min{\sum_{i=1}^{k}\sum_{j=1}^{i-1} x_i -x_j} \]这玩意可以看做从 \(n\) 个点排序后中取得一个 \(k\) 个点的子序列，算上述式子最佳答案的 \(k\) 个点。
每选择一个点，假设它是第 \(t+1\) 个点，那么我们发现，会增加这第 \(t+1\) 个点与前面 \(t\) 个点距离之和的贡献，越往左走，这个贡献越小，最左不能超过第 \(t\) 个点，所以我们有贪心策略，让这 \(k\) 个点尽量挨着，从子序列的选择，变为了子数组的选择。
接下来其实就类似滑动窗口，枚举起点，算出贡献，比较即可。
先考虑多一个数的贡献：
\[\sum_{j=l}^{r-1} x_r-x_j=(r-l)\times x_r-\sum_{j=l}^{r-1}x_j \]\[前缀和优化:\ \sum_{j=l}^{r-1}x_j=pre[r-1]-pre[l-1] \]
少一个数的贡献：
\[窗口满时移动:\ \sum_{j=l+1}^{r} x_j-x_l=\sum_{j=l+1}^{r}x_j-(k-1)\times x_l \]\[\sum_{j=l+1}^{r}x_j=pre[r]-pre[l] \]所以滑窗转移就是 \(O(1)\)，就做完了。
参照代码
#include <bits/stdc++.h>
// #pragma GCC optimize(2)
// #pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4.1,sse4.2,avx,avx2,popcnt,tune=native")
// #define isPbdsFile
#ifdef isPbdsFile
#include <bits/extc++.h>
#else
#include <ext/pb_ds/priority_queue.hpp>
#include <ext/pb_ds/hash_policy.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/trie_policy.hpp>
#include <ext/pb_ds/tag_and_trait.hpp>
#include <ext/pb_ds/hash_policy.hpp>
#include <ext/pb_ds/list_update_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/exception.hpp>
#include <ext/rope>
#endif
using namespace std;
using namespace __gnu_cxx;
using namespace __gnu_pbds;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef tuple<int, int, int> tii;
typedef tuple<ll, ll, ll> tll;
typedef unsigned int ui;
typedef unsigned long long ull;
#define hash1 unordered_map
#define hash2 gp_hash_table
#define hash3 cc_hash_table
#define stdHeap std::priority_queue
#define pbdsHeap __gnu_pbds::priority_queue
#define sortArr(a, n) sort(a+1,a+n+1)
#define all(v) v.begin(),v.end()
#define yes cout<<"YES"
#define no cout<<"NO"
#define Spider ios_base::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);
#define MyFile freopen("..\\input.txt", "r", stdin),freopen("..\\output.txt", "w", stdout);
#define forn(i, a, b) for(int i = a; i <= b; i++)
#define forv(i, a, b) for(int i=a;i>=b;i--)
#define ls(x) (x<<1)
#define rs(x) (x<<1|1)
#define endl '\n'
//用于Miller-Rabin
[[maybe_unused]] static int Prime_Number[13] = {0, 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37};
template <typename T>
int disc(T* a, int n)
{
return unique(a + 1, a + n + 1) - (a + 1);
}
template <typename T>
T lowBit(T x)
{
return x & -x;
}
template <typename T>
T Rand(T l, T r)
{
static mt19937 Rand(time(nullptr));
uniform_int_distribution<T> dis(l, r);
return dis(Rand);
}
template <typename T1, typename T2>
T1 modt(T1 a, T2 b)
{
return (a % b + b) % b;
}
template <typename T1, typename T2, typename T3>
T1 qPow(T1 a, T2 b, T3 c)
{
a %= c;
T1 ans = 1;
for (; b; b >>= 1, (a *= a) %= c) if (b & 1) (ans *= a) %= c;
return modt(ans, c);
}
template <typename T>
void read(T& x)
{
x = 0;
T sign = 1;
char ch = getchar();
while (!isdigit(ch))
{
if (ch == '-') sign = -1;
ch = getchar();
}
while (isdigit(ch))
{
x = (x << 3) + (x << 1) + (ch ^ 48);
ch = getchar();
}
x *= sign;
}
template <typename T, typename... U>
void read(T& x, U&... y)
{
read(x);
read(y...);
}
template <typename T>
void write(T x)
{
if (typeid(x) == typeid(char)) return;
if (x < 0) x = -x, putchar('-');
if (x > 9) write(x / 10);
putchar(x % 10 ^ 48);
}
template <typename C, typename T, typename... U>
void write(C c, T x, U... y)
{
write(x), putchar(c);
write(c, y...);
}
template <typename T11, typename T22, typename T33>
struct T3
{
T11 one;
T22 tow;
T33 three;
bool operator<(const T3 other) const
{
if (one == other.one)
{
if (tow == other.tow) return three < other.three;
return tow < other.tow;
}
return one < other.one;
}
T3()
{
one = tow = three = 0;
}
T3(T11 one, T22 tow, T33 three) : one(one), tow(tow), three(three)
{
}
};
template <typename T1, typename T2>
void uMax(T1& x, T2 y)
{
if (x < y) x = y;
}
template <typename T1, typename T2>
void uMin(T1& x, T2 y)
{
if (x > y) x = y;
}
constexpr int N = 3e5 + 10;
pll a[N];
int n, k;
ll pre[N];
ll curr, mi = LLONG_MAX;
int ansIdx;
inline void solve()
{
cin >> n;
forn(i, 1, n) cin >> a[i].first, a[i].second = i;
sortArr(a, n);
forn(i, 1, n) pre[i] = pre[i - 1] + a[i].first;
cin >> k;
ll l = 1;
forn(r, 1, n)
{
curr += (r - l) * a[r].first - (pre[r - 1] - pre[l - 1]);
if (r >= k)
{
if (curr < mi) mi = curr, ansIdx = l;
curr -= pre[r] - pre[l] - (k - 1) * a[l++].first;
}
}
while (k--) cout << a[ansIdx++].second << ' ';
}
signed int main()
{
// MyFile
Spider
//------------------------------------------------------
// clock_t start = clock();
int test = 1;
// read(test);
// cin >> test;
forn(i, 1, test) solve();
// while (cin >> n, n)solve();
// while (cin >> test)solve();
// clock_t end = clock();
// cerr << "time = " << double(end - start) / CLOCKS_PER_SEC << "s" << endl;
}