Submission #219140

#	Time	Username	Problem	Language	Result	Execution time	Memory
219140		peuch	Islands (IOI08_islands)	C++17	18 / 100	1192 ms	131076 KiB

islands

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

const int MAXN = 1000010;

int n;
int rep;
int in[MAXN];
long long prof[MAXN], dist[MAXN];
vector<int> ar[MAXN], wg[MAXN];
bool isCycle[MAXN], marc[MAXN];
long long ans;

void getCycle();

int dfs1(int cur){
	marc[cur] = 1;
	int ret = cur;
	for(int i = 0; i < ar[cur].size(); i++){
		int viz = ar[cur][i];
		if(in[viz]) continue;
		if(marc[viz]) continue;
		dist[viz] = dist[cur] + wg[cur][i];
		int aux = dfs1(viz);
		if(dist[aux] > dist[ret]) ret = aux;
	}
	return ret;
}
 
long long dfs2(int cur){
	marc[cur] = 0;
	long long ret = dist[cur];
	for(int i = 0; i < ar[cur].size(); i++){
		int viz = ar[cur][i];
		if(isCycle[viz] && viz != rep) continue;
		if(!marc[viz]) continue;
		dist[viz] = dist[cur] + wg[cur][i];
		ret = max(ret, dfs2(viz));
	}
	return ret;
}

int main(){
	scanf("%d", &n);
	for(int i = 1; i <= n; i++){
		int aux1, aux2;
		scanf("%d %d", &aux1, &aux2);
		in[aux1]++;
		ar[aux1].push_back(i);
		ar[i].push_back(aux1);
		wg[i].push_back(aux2);
		wg[aux1].push_back(aux2);
	}
	getCycle();
	printf("%lld\n", ans);
}

void getCycle(){
	int fila[n];
	int fim = 0;
	int ini = 0;
	for(int i = 1; i <= n; i++)	
		if(in[i] == 0) fila[fim++] = i;
	while(ini != fim){
		int cur = fila[ini++];
		for(int j = 0; j < ar[cur].size(); j++){
			int viz = ar[cur][j];
			if(in[viz] == 0) continue;
			in[viz]--;
			prof[viz] = max(prof[viz], prof[cur] + wg[cur][j]);
			if(in[viz] == 0) fila[fim++] = viz;
		}
	}
	for(int i = 1; i <= n; i++){
		if(!in[i] || isCycle[i]) continue;
		int cur = i;
		dist[cur] = 0;
		int cnt = 0;
		int last = 0;
		long long aux = 0;
		long long sct = 0;
		while(1){
			last = cur;
			cnt++;
			isCycle[cur] = 1;
			rep = cur;
			long long auxDist = dist[cur];
			dist[cur] = 0;
			int x = dfs1(cur);
			dist[x] = 0;
			aux = max(aux, dfs2(x));
			dist[cur] = auxDist;
			bool flag = true;
			for(int j = 0; j < ar[cur].size(); j++){
				int viz = ar[cur][j];
				if(!in[viz] || isCycle[viz]) continue;
				dist[viz] = dist[cur] + wg[cur][j];
				sct += wg[cur][i];
				cur = viz;
				flag = false;
				break;
			}
			if(flag) break;
		}
		if(cnt == 1){
			ans += aux;
			continue;
		}
		if(cnt == 2){
			sct = 0;
			for(int j = 0; j < ar[i].size(); j++) 
				if(isCycle[ar[i][j]]) sct += wg[i][j];
		}
		else{
			for(int j = 0; j < ar[cur].size(); j++) 
				if(ar[cur][j] == i) sct += wg[i][j];
		}
		long long aux2 = prof[cur] + dist[cur];
		long long aux3 = prof[cur] - dist[cur];
		if(cnt == 2) cur = i;
		else{
			for(int j = 0; j < ar[cur].size(); j++) {
				int viz = ar[cur][j];
				if(!isCycle[viz]) continue;
				if(dist[viz] > dist[cur] || viz == i) continue;
				cur = viz;
				break;
			}
		}
		while(1){
			aux = max(aux, aux2 + prof[cur] - dist[cur]);
			aux = max(aux, aux3 + sct + prof[cur] + dist[cur]);
			aux2 = max(aux2, prof[cur] + dist[cur]);
			aux3 = max(aux3, prof[cur] - dist[cur]);
			bool flag = true;
			for(int j = 0; j < ar[cur].size(); j++) {
				int viz = ar[cur][j];
				if(!isCycle[viz]) continue;
				if(dist[viz] > dist[cur]) continue;
				cur = viz;
				flag = false;
				break;
			}
			if(flag) break;
		}
		if(cnt == 2) cur = last;
		else{
			for(int j = 0; j < ar[cur].size(); j++) {
				int viz = ar[cur][j];
				if(!isCycle[viz]) continue;
				if(dist[viz] < dist[cur] || viz == last) continue;
				cur = viz;
				break;
			}
		}
		aux2 = prof[i] - dist[i];
		aux3 = prof[i] + dist[i];
		while(1){
			if(cur == i) break;
			aux = max(aux, aux2 + prof[cur] + dist[cur]);
			aux = max(aux, aux3 + sct + prof[cur] - dist[cur]);
			aux2 = max(aux2, prof[cur] - dist[cur]);
			aux3 = max(aux3, prof[cur] + dist[cur]);
			bool flag = true;
			for(int j = 0; j < ar[cur].size(); j++) {
				int viz = ar[cur][j];
				if(!isCycle[viz]) continue;
				if(dist[viz] < dist[cur]) continue;
				cur = viz;
				flag = false;
				break;
			}
			if(flag) break;
		}
		ans += aux;
	}
}

Compilation message (stderr)

islands.cpp: In function 'int dfs1(int)':
islands.cpp:19:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 0; i < ar[cur].size(); i++){
                 ~~^~~~~~~~~~~~~~~~
islands.cpp: In function 'long long int dfs2(int)':
islands.cpp:33:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 0; i < ar[cur].size(); i++){
                 ~~^~~~~~~~~~~~~~~~
islands.cpp: In function 'void getCycle()':
islands.cpp:66:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int j = 0; j < ar[cur].size(); j++){
                  ~~^~~~~~~~~~~~~~~~
islands.cpp:94:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int j = 0; j < ar[cur].size(); j++){
                   ~~^~~~~~~~~~~~~~~~
islands.cpp:111:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int j = 0; j < ar[i].size(); j++) 
                   ~~^~~~~~~~~~~~~~
islands.cpp:115:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int j = 0; j < ar[cur].size(); j++) 
                   ~~^~~~~~~~~~~~~~~~
islands.cpp:122:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int j = 0; j < ar[cur].size(); j++) {
                   ~~^~~~~~~~~~~~~~~~
islands.cpp:136:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int j = 0; j < ar[cur].size(); j++) {
                   ~~^~~~~~~~~~~~~~~~
islands.cpp:148:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int j = 0; j < ar[cur].size(); j++) {
                   ~~^~~~~~~~~~~~~~~~
islands.cpp:165:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int j = 0; j < ar[cur].size(); j++) {
                   ~~^~~~~~~~~~~~~~~~
islands.cpp: In function 'int main()':
islands.cpp:44:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d", &n);
  ~~~~~^~~~~~~~~~
islands.cpp:47:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d %d", &aux1, &aux2);
   ~~~~~^~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 15 / 33
• Subtask 2: 3 / 3
• Subtask 3: 0 / 4
• Subtask 4: 0 / 10
• Subtask 5: 0 / 10
• Subtask 6: 0 / 10
• Subtask 7: 0 / 10
• Subtask 8: 0 / 10
• Subtask 9: 0 / 10