Submission #1027528

#	Time	Username	Problem	Language	Result	Execution time	Memory
1027528		toan2602	One-Way Streets (CEOI17_oneway)	C++14	0 / 100	1 ms	6744 KiB

oneway

#include<bits/stdc++.h>

using namespace std;
int n, m, p, u, v, lead[100005], low[100005], num[100005], d = 0, cnt = 0, ans[100005], timer = 0, q, val[100005];
vector<pair<int,int>> adj[100005];
vector<pair<int,int>> adj2[100005], edge;
stack<int> s;
void dfs(int u, int id) {
	low[u] = num[u] = ++d;
	s.push(u);
	for (pair<int, int> W: adj[u]) {
		int node = W.first;
		if(W.second == id) continue;
		if(num[node] != 0) low[u] = min(low[u], num[node]);
		else {
			dfs(node, W.second);
			low[u] = min(low[u], low[node]);
		}
	}
	if(low[u] == num[u]) {
		cnt++;
		while(s.top() != u) lead[s.top()] = cnt, s.pop();
		lead[s.top()] = cnt, s.pop();
	}
}
void cal(int u, int par) {
	for (pair<int, int> node: adj2[u]) {
		if(node.first == par) continue;
		cal(node.first, u);
		val[u] += val[node.first];
	}
}
void get_ans(int u, int par) {
	for (pair<int, int> node: adj2[u]) {
		if(node.first == par) continue;
		int x, y;
		x = u, y = node.first;
		int id = node.second;
		if(val[node.first] < 0) {
			if(lead[edge[id].first] == x && lead[edge[id].second] == y) ans[id+1] = 1;
			else ans[id+1] = 2;
		}
		else if(val[node.first] > 0) {
			if(lead[edge[id].first] == x && lead[edge[id].second] == y) ans[id+1] = 2;
			else ans[id+1] = 1;
		}
		else ans[id+1] = 0;
		get_ans(node.first, u);
	}
}
void solve() {
	cin >> n >> m;
	for (int i = 1; i <= m; i++) {
		cin >> u >> v;
		edge.push_back({u,v});
		adj[u].push_back({v,i});
		adj[v].push_back({u,i});
	}
	dfs(1, -1);
	int idx = 0;
	for (pair<int, int> i: edge) {
		if(lead[i.first] != lead[i.second]) adj2[lead[i.first]].push_back({lead[i.second], idx}), adj2[lead[i.second]].push_back({lead[i.first],idx});
		idx++;
	}
	cin >> q;
	while(q--) {
		cin >> u >> v;
		u = lead[u];
		v = lead[v];
		val[u]++;
		val[v]--;
	}
	cal(1,-1);
	get_ans(1, -1);
	for (int i = 1; i <= m; i++) if(ans[i] == 0) cout << 'B'; else if(ans[i] == 1) cout << 'R'; else cout << 'L';
}

signed main() {
	ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
	if(fopen("input.inp","r")){
		freopen("input.inp", "r", stdin);
		freopen("output.out", "w", stdout);
	}
	int t = 1;
	// cin >> t;
	while(t--) {
		solve();
	}
}

Compilation message (stderr)

oneway.cpp: In function 'int main()':
oneway.cpp:81:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   81 |   freopen("input.inp", "r", stdin);
      |   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
oneway.cpp:82:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   82 |   freopen("output.out", "w", stdout);
      |   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 30
• Subtask 2: 0 / 30
• Subtask 3: 0 / 40