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ID题目提交者结果用时内存语言文件大小提交时间测评时间
#241008#6560. Broken Minimum Spanning TreeMovingUp#WA 2ms3476kbC++143.1kb2023-11-05 21:52:242023-11-05 21:52:24

Judging History

你现在查看的是最新测评结果

  • [2023-11-05 21:52:24]
  • 评测
  • 测评结果:WA
  • 用时:2ms
  • 内存:3476kb
  • [2023-11-05 21:52:24]
  • 提交

answer

#include <bits/stdc++.h>

using namespace std;

struct edge {
  int id;
  int u, v, w;

  bool operator<(const edge &o) const { 
	if (w == o.w) {
		return id < o.id;
	}
	return w < o.w; 
  }
};

struct dsu {
  vector<int> parent, subtree;

  void init(int n) {
    parent.resize(n);
    subtree.resize(n);

    for (int i = 0; i < n; i++) {
      subtree[i] = 1;
      parent[i] = i;
    }
  }

  int findParent(int x) {
    if (parent[x] == x)
      return x;
    else {
      parent[x] = findParent(parent[x]);
      return parent[x];
    }
  }

  void unite(int parX, int parY) {
    if (subtree[parX] < subtree[parY]) {
      parent[parX] = parY;
      subtree[parY] += subtree[parX];
    } else {
      parent[parY] = parX;
      subtree[parX] += subtree[parY];
    }
  }
};

int64_t findMst(int n, const vector<edge> &edges, int edgeId) {
  dsu d;
  d.init(n);

  int64_t ans = 0;
  for (auto e : edges) {
    if (e.id == edgeId) {
      ans += e.w;
      d.unite(e.u, e.v);
    }
  }

  for (auto e : edges) {
    if (e.id == edgeId) {
      continue;
    }

    int parX = d.findParent(e.u);
    int parY = d.findParent(e.v);

    if (parX != parY) {
      ans += e.w;
      d.unite(parX, parY);
    }
  }

  return ans;
}

int findReplacement(int n, const vector<edge> &edges, vector<bool>& forced) {
  dsu d;
  d.init(n);

  for (auto e : edges) {
    if (forced[e.id]) {
      d.unite(e.u, e.v);
    }
  }

  for (auto e : edges) {
    if (forced[e.id]) {
      continue;
    }

    int parX = d.findParent(e.u);
    int parY = d.findParent(e.v);

    if (parX != parY) {
	  return e.id;
    }
  }

  assert(false);
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);

  int n, m;
  cin >> n >> m;

  vector<edge> edges(m);
  for (int i = 0; i < m; i++) {
    int u, v, w;
    cin >> u >> v >> w;

    u--;
    v--;

    edges[i] = {i, u, v, w};
  }

  sort(edges.begin(), edges.end());

  int64_t globalMst = findMst(n, edges, -1);

  vector<bool> keep(n - 1, false);

  {
	dsu d;
	d.init(n);

	int64_t ans = 0;

	for (auto e : edges) {
		int parX = d.findParent(e.u);
		int parY = d.findParent(e.v);

		if (parX != parY) {
			ans += e.w;
			d.unite(parX, parY);
			if (e.id < n - 1) {
				keep[e.id] = true;
			}
		}
	}
  }

  vector<bool> forced(m);
  vector<int> removals;
  for (int i = 0; i < n - 1; i++) {
	forced[i] = true;
	if (!keep[i]) {
		removals.push_back(i);
	}
  }

  vector<pair<int, int>> changes;
  while (!removals.empty()) {
	int id = removals.back();
	removals.pop_back();

	forced[id] = false;
	int replacement = findReplacement(n, edges, forced);
	forced[replacement] = true;
	changes.push_back({id, replacement});
  }

  int64_t newMst = 0;
  for (int i = 0; i < m; i++) {
	edge e = edges[i];
	if (forced[e.id]) {
		newMst += e.w;
	}
  }

//   if (newMst != globalMst) {
// 	assert(false);
//   }

  cout << changes.size() << endl;
  for (auto [x, y] : changes) {
    cout << x + 1 << " " << y + 1 << endl;
  }
}

詳細信息

Test #1:

score: 100
Accepted
time: 1ms
memory: 3464kb

input:

4 4
1 2 10
2 3 3
3 4 1
1 4 4

output:

1
1 4

result:

ok correct!

Test #2:

score: 0
Accepted
time: 0ms
memory: 3460kb

input:

6 8
1 2 10
2 3 10
3 4 10
4 5 10
5 6 10
6 1 10
1 3 1
4 6 1

output:

2
5 8
2 7

result:

ok correct!

Test #3:

score: 0
Accepted
time: 1ms
memory: 3476kb

input:

2000 1999
1262 1505 968661582
323 1681 787089412
1132 129 88786681
1909 587 762050278
979 1371 230688681
1686 521 980519364
975 191 887826021
869 461 899130441
1433 259 961154249
1718 547 721696188
1254 1042 458319755
1779 267 85751052
1170 813 283230029
309 20 971682908
224 417 255325364
1084 986 7...

output:

0

result:

ok correct!

Test #4:

score: 0
Accepted
time: 0ms
memory: 3448kb

input:

1999 1998
1757 1820 444157563
1757 395 754598547
1757 1571 432619009
1757 1009 456234067
1757 824 935569725
1757 1698 476714469
1757 1420 901765343
1757 1175 225295107
1757 1512 721959801
1757 1585 955067704
1757 1739 635181418
1757 1686 891225461
1757 84 132683224
1757 1696 48915557
1757 1623 42602...

output:

0

result:

ok correct!

Test #5:

score: 0
Accepted
time: 1ms
memory: 3444kb

input:

1999 1998
1345 647 232183406
40 837 279910457
819 857 137486924
255 1378 517489941
827 1565 894953662
1556 1545 898170464
965 877 72248541
1631 298 635713424
895 197 366305735
966 1160 515776809
1870 1638 220711661
1736 220 716014108
1914 1609 759121968
1293 153 272816132
1936 1433 263859075
985 460...

output:

0

result:

ok correct!

Test #6:

score: 0
Accepted
time: 1ms
memory: 3448kb

input:

500 998
105 1 1
105 2 1
105 3 1
105 4 1
105 5 1
105 6 1
105 7 1
105 8 1
105 9 1
105 10 1
105 11 1
105 12 1
105 13 1
105 14 1
105 15 1
105 16 1
105 17 1
105 18 1
105 19 1
105 20 1
105 21 1
105 22 1
105 23 1
105 24 1
105 25 1
105 26 1
105 27 1
105 28 1
105 29 1
105 30 1
105 31 1
105 32 1
105 33 1
105 ...

output:

0

result:

ok correct!

Test #7:

score: 0
Accepted
time: 1ms
memory: 3392kb

input:

500 998
364 1 1
364 2 1
364 3 1
364 4 1
364 5 1
364 6 1
364 7 1
364 8 1
364 9 1
364 10 1
364 11 1
364 12 1
364 13 1
364 14 1
364 15 1
364 16 1
364 17 1
364 18 1
364 19 1
364 20 1
364 21 1
364 22 1
364 23 1
364 24 1
364 25 1
364 26 1
364 27 1
364 28 1
364 29 1
364 30 1
364 31 1
364 32 1
364 33 1
364 ...

output:

0

result:

ok correct!

Test #8:

score: -100
Wrong Answer
time: 2ms
memory: 3460kb

input:

500 998
86 1 2
86 2 2
86 3 2
86 4 2
86 5 2
86 6 2
86 7 2
86 8 2
86 9 2
86 10 2
86 11 2
86 12 2
86 13 2
86 14 2
86 15 2
86 16 2
86 17 2
86 18 2
86 19 2
86 20 2
86 21 2
86 22 2
86 23 2
86 24 2
86 25 2
86 26 2
86 27 2
86 28 2
86 29 2
86 30 2
86 31 2
86 32 2
86 33 2
86 34 2
86 35 2
86 36 2
86 37 2
86 38...

output:

499
499 998
498 997
497 996
496 500
495 501
494 502
493 503
492 504
491 505
490 506
489 507
488 508
487 509
486 510
485 511
484 512
483 513
482 514
481 515
480 516
479 517
478 518
477 519
476 520
475 521
474 522
473 523
472 524
471 525
470 526
469 527
468 528
467 529
466 530
465 531
464 532
463 533
...

result:

wrong answer not a spanning tree after swap 5