I. Array Negations

Array Negations.cpp

/**
 *  Author  : Pnictogen
 *  Task    :
 *  Algo    :
**/
#include <bits/stdc++.h>

#define endl          '\n'
#define sqr(x)        (x) * (x)
#define gcd(x,y)      __gcd(x,y)
#define lcm(x,y)      ((x/gcd(x,y)) * y)
#define sz(x)         (int)x.size()
#define all(x)        (x).begin(),(x).end()
#define rall(x)       (x).rbegin(),(x).rend()
#define prec(x)       fixed<<setprecision(x)
#define min3(a,b,c)   min(a,min(b,c))
#define max3(a,b,c)   max(a,max(b,c))
#define min4(a,b,c,d) min(a,min(b,min(c,d)))
#define max4(a,b,c,d) max(a,max(b,max(c,d)))
#define unsyncIO      ios_base::sync_with_stdio(false); cin.tie(nullptr)

using namespace std;
using ll = long long;
using db = double;
using ld = long double;
using ull = unsigned long long;

const ld PI = acos((ld) - 1);
const int MOD = 1e9 + 7;
const ll INF = 2e18 + 1;
const ld EPS = 1e-9;
const int MX = 2e5;

#ifdef LOCAL
#include"debug.h"
#else
#define debug(...)
#endif
// Note : Each element in the array can be negated multiple times.
void solve() {
	int n, k, pos = 0;	cin >> n >> k;
	vector <int> v(n);
	for (int i = 0; i < n; i++) cin >> v[i];
	sort(v.begin(), v.end());
	ll sum = 0;
	for (int i = 0; i < k; i++) {
		if (v[i] <= 0) {
			v[i] = -v[i];
			pos++; // count how many negatiove we made positive
		} else break;
	}
	k = (k - pos) % 2; // if we negation twice of a element it remains same.
	if (k == 1) {// if k is 1 then we make the smallest negation so that the sum is max
		sort(v.begin(), v.end());
		v[0] = -v[0];
	}

	sum = accumulate(v.begin(), v.end(), 0ll);
	/*for (int data : v) cout << data << " ";
	cout << endl;*/
	cout << sum << endl;

}

int main() {

#ifdef LOCAL
	clock_t tStart = clock();
	freopen("in.txt", "r", stdin);
	freopen("out.txt", "w", stdout);
#endif
	unsyncIO;

	int t = 1;	cin >> t;

	while (t--) {
		solve();
	}

#ifdef LOCAL
	cerr << "\nRuntime: " << (ld) (clock() - tStart) / CLOCKS_PER_SEC << " Seconds" << endl;
#endif
	return 0;
}