제출 #103658

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
103658		KCSC	Islands (IOI08_islands)	C++14	80 / 100	1470 ms	132096 KiB

islands

// 22.48
#include <bits/stdc++.h>
using namespace std;

const int DIM = 1000005;

long long dst[DIM];
int oki[DIM], lev[DIM], cst[DIM], fth[DIM];

vector<int> cyc, val; 
vector<long long> dpl, dpr;
vector<pair<int, int>> edg[DIM];

void dfs1(int x, int f) {
	oki[x] = true; lev[x] = lev[f] + 1;
	bool ok = false;
	for (auto it : edg[x]) {
		int y = it.first, c = it.second;
		if (!oki[y]) {
			cst[y] = c; fth[y] = x; dfs1(y, x); }
		else if (lev[y] < lev[x] and (y != f or ok)) {
			for (int z = x; z != fth[y]; z = fth[z]) {
				oki[z] = 2; cyc.push_back(z);  
				if (z == y) {
					val.push_back(c); }
				else {
					val.push_back(cst[z]); } } } 
		if (y == f) {
			ok = true; } } }

void dfs2(int x, int f, int &nd, long long &ds) {
	if (ds < dst[x]) {
		ds = dst[x]; nd = x; }
	for (auto it : edg[x]) {
		int y = it.first, c = it.second;
		if (oki[y] == 2 or y == f) {
			continue; }
		dst[y] = dst[x] + c; dfs2(y, x, nd, ds); } }

int main(void) {
#ifdef HOME
	freopen("islands.in", "r", stdin);
	freopen("islands.out", "w", stdout);
#endif
	int n; cin >> n;
	for (int i = 1; i <= n; ++i) {
		int y, c; cin >> y >> c;
		edg[i].push_back(make_pair(y, c)); 
		edg[y].push_back(make_pair(i, c)); }
	long long ans = 0;
	for (int k = 1; k <= n; ++k) {
		if (oki[k]) {
			continue; }
		cyc.clear(); val.clear(); dfs1(k, 0); 
		long long aux = 0; int m = cyc.size();
		dpl.resize(m); dpr.resize(m);
		dpl[0] = 0;
		for (int i = 1; i < m; ++i) {
			dpl[i] = dpl[i - 1] + val[i - 1]; }
		dpr[m - 1] = val[m - 1];
		for (int i = m - 2; i >= 0; --i) {
				dpr[i] = dpr[i + 1] + val[i]; }
		long long cs1 = -1LL << 60, cs2 = -1LL << 60;
		for (int i = 0; i < m; ++i) {
			int x = cyc[i]; oki[x] = 1;
			int c1; long long mx1 = -1; dst[x] = 0; dfs2(x, 0, c1, mx1);
			int c2; long long mx2 = -1; dst[c1] = 0; dfs2(c1, 0, c2, mx2);
			aux = max(aux, mx2); oki[x] = 2; 
			if (i) {
				aux = max(aux, cs1 + dpl[i] + mx1);
				aux = max(aux, cs2 + dpr[i] + mx1); }
			cs1 = max(cs1, mx1 - dpl[i]);
			cs2 = max(cs2, mx1 + dpl[i]); }
		ans += aux; }
	cout << ans << endl;
	return 0; }

• Subtask 1: 33 / 33
• Subtask 2: 3 / 3
• Subtask 3: 4 / 4
• Subtask 4: 10 / 10
• Subtask 5: 10 / 10
• Subtask 6: 10 / 10
• Subtask 7: 10 / 10
• Subtask 8: 0 / 10
• Subtask 9: 0 / 10