oj.uz

Submission #869442

# Submission time Handle Problem Language Result Execution time Memory
869442 2023-11-04T10:45:38 Z LeThanhMinh Network (BOI15_net) C++14
100 / 100
 650 ms 102840 KB 
// Problem: H. Hai đường đi
// Contest: Codeforces - 2023 winter contest #41, Dalat winter training camp, round 1
// URL: https://gspvh23.contest.codeforces.com/group/FIWwc7nF6c/contest/484130/problem/H
// Memory Limit: 512 MB
// Time Limit: 2250 ms
// 
// Powered by CP Editor (https://cpeditor.org)

/*CP template version 3.0 - Laconic*/

#include <bits/stdc++.h>

#define ii pair<int, int>
#define fs first
#define sc second

//use struct instead of pair<int, ii>

#define int long long

#define show(v) {for (auto i : v) cout << i << " "; cout << endl;}
#define showlr(v, l, r) {for (int i = l; i <= r; i++) cout << v[i] << " "; cout << endl;}
#define all(v) v.begin(), v.end()
#define SUnique(v) {sort(all(v)); v.erase(unique(all(v)), v.end());}
#define forlr(i, l, r) for (int i = l; i <= r; i++)
#define forrl(i, r, l) for (int i = r; i >= l; i--)

#pragma GCC Optimize("O2")
#define endl "\n"
#define precise(x) cout << fixed << setprecision(x);

using namespace std;

const int N = 5e5 + 100;
const int MOD = 1e9 + 7;
const int INF = 1e9;
const int LOG = 25;
const long long LINF = 1e15 + 100;

const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, -1, 0, 1};
 
ostream& operator << (ostream &os, ii a) {
    
    os << a.fs << ' ' << a.sc;
    return os;
    
}

int binPow(int a, int b, int m = LLONG_MAX) {
    
    int prod = 1;
    a %= m;
    
    while (b) {
        
        if (b & 1) prod = prod * a % m;
        a = a * a % m;
        b /= 2;
        
    }
    
    return prod;
    
}

void setIO(string s) {
    
    if (s.empty()) return;
    
    freopen((s + ".inp").c_str(), "r", stdin);
    freopen((s + ".out").c_str(), "w", stdout);
    
}

//Try Brute Force (maybe there is a pattern)
//Try DP (Weird constraints (sum of all elements <= 10000), small constraints)
//Try Graph (a pair of number, condition between elements)
//Try Geometry (Same as graph, for coordinate)

//Try switching between problem
//Put down what you have on paper
//IMPORTANT: WRITE DOWN THE FORMULA

int n, m, q, k;
int arr[N];
vector<int> adj[N], adj1[N];

int low[N], num[N], head[N], timeDfs;
stack<int> st;
int bccId[N], bcc;

void tarjan(int u, int pre) {
    
    st.push(u);
    num[u] = low[u] = ++timeDfs;
     
    for (int v : adj[u]) {
        
        if (v == pre) continue;
        if (num[v]) {
            
            low[u] = min(low[u], num[v]);
            
        } else {
            
            tarjan(v, u);
            low[u] = min(low[u], low[v]);
 
        }
        
    }
    
    if (num[u] == low[u]) {
        
        bcc++;
        int tmp;
        head[bcc] = u;
        
        do {
            
            tmp = st.top();
            bccId[tmp] = bcc;
            st.pop();
            num[u] = INF;
            
        } while (tmp != u);

    }
    
}

vector<int> leaf;

void dfs1(int u, int pre) {
	
	if (adj1[u].size() == 1) {
		
		leaf.push_back(u);
		if (u != pre) return;
		
	}
	
	for (int v : adj1[u]) {
		
		if (v == pre) continue;
		dfs1(v, u);
		
	}
	
}

mt19937 rng(chrono::steady_clock().now().time_since_epoch().count());

ii edges[N];

void solve() {
	
	cin >> n;
	forlr(i, 1, n) adj[i].clear(), adj1[i].clear();
	leaf.clear();
	fill(bccId + 1, bccId + n + 1, 0);
	fill(low + 1, low + n + 1, 0);
	fill(num + 1, num + n + 1, 0);
	fill(head + 1, head + n + 1, 0);
	timeDfs = 0;
	bcc = 0;
	while (st.size()) st.pop();
	
	forlr(i, 1, n - 1) {
		
		int u, v; cin >> u >> v;
		edges[i] = {u, v};
		adj[u].push_back(v);
		adj[v].push_back(u);
		
	}
	
	tarjan(1, 1);
		
	forlr(i, 1, n - 1) {
		
		auto [u, v] = edges[i];			
		int idU = bccId[u], idV = bccId[v];
		if (idU == idV) continue;
		adj1[idU].push_back(idV);
		adj1[idV].push_back(idU);
		
	}
	
	forlr(i, 1, n) SUnique(adj1[i]);
	
	dfs1(1, 1);
	
	vector<ii> res;
	
	int sz = leaf.size();
	if (sz == 2) {
		
		cout << 1 << endl;
		cout << head[leaf[0]] << " " << head[leaf[1]] << endl;
		return;
		
	}
	
	if (sz <= 1) {
		
		cout << 0 << endl;
		return;
		
	}
	
	forlr(i, 0, (sz - 1) / 2) res.push_back({head[leaf[i]], head[leaf[i + sz / 2]]});
	
	cout << res.size() << endl;
	for (ii i : res) cout << i << endl;
    
}

signed main() {
    
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);    
    // setIO("biconnected");
    
    int T = 1;
    
    bool multiTest = 0;
    if (multiTest) cin >> T;
        
    while (T--) {
        
        solve();
    
    }
    
}

Compilation message

net.cpp:28: warning: ignoring '#pragma GCC Optimize' [-Wunknown-pragmas]
   28 | #pragma GCC Optimize("O2")
      | 
net.cpp: In function 'void solve()':
net.cpp:183:8: warning: structured bindings only available with '-std=c++17' or '-std=gnu++17'
  183 |   auto [u, v] = edges[i];
      |        ^
net.cpp: In function 'void setIO(std::string)':
net.cpp:71:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   71 |     freopen((s + ".inp").c_str(), "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
net.cpp:72:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   72 |     freopen((s + ".out").c_str(), "w", stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Subtask #1
18.0 / 18.0

# Verdict Execution time Memory Grader output
1 Correct 6 ms 33112 KB Output is correct
2 Correct 6 ms 33116 KB Output is correct
3 Correct 8 ms 33116 KB Output is correct
4 Correct 7 ms 33116 KB Output is correct
5 Correct 7 ms 33116 KB Output is correct
6 Correct 6 ms 33116 KB Output is correct
7 Correct 6 ms 33116 KB Output is correct
8 Correct 8 ms 33116 KB Output is correct
9 Correct 7 ms 33116 KB Output is correct
10 Correct 6 ms 33116 KB Output is correct
11 Correct 7 ms 33116 KB Output is correct
12 Correct 8 ms 33112 KB Output is correct
13 Correct 6 ms 33112 KB Output is correct
14 Correct 6 ms 33116 KB Output is correct
15 Correct 6 ms 33288 KB Output is correct
16 Correct 7 ms 33112 KB Output is correct
17 Correct 6 ms 33220 KB Output is correct
18 Correct 6 ms 33116 KB Output is correct
19 Correct 6 ms 33112 KB Output is correct
20 Correct 6 ms 33116 KB Output is correct

Subtask #2
45.0 / 45.0

# Verdict Execution time Memory Grader output
1 Correct 6 ms 33112 KB Output is correct
2 Correct 6 ms 33116 KB Output is correct
3 Correct 8 ms 33116 KB Output is correct
4 Correct 7 ms 33116 KB Output is correct
5 Correct 7 ms 33116 KB Output is correct
6 Correct 6 ms 33116 KB Output is correct
7 Correct 6 ms 33116 KB Output is correct
8 Correct 8 ms 33116 KB Output is correct
9 Correct 7 ms 33116 KB Output is correct
10 Correct 6 ms 33116 KB Output is correct
11 Correct 7 ms 33116 KB Output is correct
12 Correct 8 ms 33112 KB Output is correct
13 Correct 6 ms 33112 KB Output is correct
14 Correct 6 ms 33116 KB Output is correct
15 Correct 6 ms 33288 KB Output is correct
16 Correct 7 ms 33112 KB Output is correct
17 Correct 6 ms 33220 KB Output is correct
18 Correct 6 ms 33116 KB Output is correct
19 Correct 6 ms 33112 KB Output is correct
20 Correct 6 ms 33116 KB Output is correct
21 Correct 7 ms 33116 KB Output is correct
22 Correct 7 ms 33288 KB Output is correct
23 Correct 7 ms 33476 KB Output is correct
24 Correct 7 ms 33388 KB Output is correct
25 Correct 7 ms 33372 KB Output is correct
26 Correct 7 ms 33372 KB Output is correct
27 Correct 7 ms 33368 KB Output is correct
28 Correct 7 ms 33372 KB Output is correct
29 Correct 8 ms 33624 KB Output is correct
30 Correct 7 ms 33112 KB Output is correct
31 Correct 7 ms 33368 KB Output is correct
32 Correct 7 ms 33116 KB Output is correct
33 Correct 6 ms 33112 KB Output is correct
34 Correct 6 ms 33116 KB Output is correct
35 Correct 6 ms 33116 KB Output is correct
36 Correct 7 ms 33296 KB Output is correct
37 Correct 7 ms 33372 KB Output is correct
38 Correct 7 ms 33372 KB Output is correct
39 Correct 7 ms 33116 KB Output is correct
40 Correct 7 ms 33116 KB Output is correct
41 Correct 7 ms 33112 KB Output is correct
42 Correct 11 ms 33116 KB Output is correct
43 Correct 7 ms 33376 KB Output is correct
44 Correct 6 ms 33116 KB Output is correct
45 Correct 11 ms 33116 KB Output is correct
46 Correct 7 ms 33368 KB Output is correct
47 Correct 6 ms 33116 KB Output is correct
48 Correct 6 ms 33116 KB Output is correct
49 Correct 7 ms 33372 KB Output is correct
50 Correct 6 ms 33116 KB Output is correct
51 Correct 6 ms 33232 KB Output is correct
52 Correct 7 ms 33116 KB Output is correct
53 Correct 7 ms 33372 KB Output is correct
54 Correct 6 ms 33116 KB Output is correct
55 Correct 6 ms 33116 KB Output is correct
56 Correct 6 ms 33116 KB Output is correct
57 Correct 7 ms 33372 KB Output is correct
58 Correct 7 ms 33372 KB Output is correct

Subtask #3
37.0 / 37.0

# Verdict Execution time Memory Grader output
1 Correct 6 ms 33112 KB Output is correct
2 Correct 6 ms 33116 KB Output is correct
3 Correct 8 ms 33116 KB Output is correct
4 Correct 7 ms 33116 KB Output is correct
5 Correct 7 ms 33116 KB Output is correct
6 Correct 6 ms 33116 KB Output is correct
7 Correct 6 ms 33116 KB Output is correct
8 Correct 8 ms 33116 KB Output is correct
9 Correct 7 ms 33116 KB Output is correct
10 Correct 6 ms 33116 KB Output is correct
11 Correct 7 ms 33116 KB Output is correct
12 Correct 8 ms 33112 KB Output is correct
13 Correct 6 ms 33112 KB Output is correct
14 Correct 6 ms 33116 KB Output is correct
15 Correct 6 ms 33288 KB Output is correct
16 Correct 7 ms 33112 KB Output is correct
17 Correct 6 ms 33220 KB Output is correct
18 Correct 6 ms 33116 KB Output is correct
19 Correct 6 ms 33112 KB Output is correct
20 Correct 6 ms 33116 KB Output is correct
21 Correct 7 ms 33116 KB Output is correct
22 Correct 7 ms 33288 KB Output is correct
23 Correct 7 ms 33476 KB Output is correct
24 Correct 7 ms 33388 KB Output is correct
25 Correct 7 ms 33372 KB Output is correct
26 Correct 7 ms 33372 KB Output is correct
27 Correct 7 ms 33368 KB Output is correct
28 Correct 7 ms 33372 KB Output is correct
29 Correct 8 ms 33624 KB Output is correct
30 Correct 7 ms 33112 KB Output is correct
31 Correct 7 ms 33368 KB Output is correct
32 Correct 7 ms 33116 KB Output is correct
33 Correct 6 ms 33112 KB Output is correct
34 Correct 6 ms 33116 KB Output is correct
35 Correct 6 ms 33116 KB Output is correct
36 Correct 7 ms 33296 KB Output is correct
37 Correct 7 ms 33372 KB Output is correct
38 Correct 7 ms 33372 KB Output is correct
39 Correct 7 ms 33116 KB Output is correct
40 Correct 7 ms 33116 KB Output is correct
41 Correct 7 ms 33112 KB Output is correct
42 Correct 11 ms 33116 KB Output is correct
43 Correct 7 ms 33376 KB Output is correct
44 Correct 6 ms 33116 KB Output is correct
45 Correct 11 ms 33116 KB Output is correct
46 Correct 7 ms 33368 KB Output is correct
47 Correct 6 ms 33116 KB Output is correct
48 Correct 6 ms 33116 KB Output is correct
49 Correct 7 ms 33372 KB Output is correct
50 Correct 6 ms 33116 KB Output is correct
51 Correct 6 ms 33232 KB Output is correct
52 Correct 7 ms 33116 KB Output is correct
53 Correct 7 ms 33372 KB Output is correct
54 Correct 6 ms 33116 KB Output is correct
55 Correct 6 ms 33116 KB Output is correct
56 Correct 6 ms 33116 KB Output is correct
57 Correct 7 ms 33372 KB Output is correct
58 Correct 7 ms 33372 KB Output is correct
59 Correct 410 ms 93016 KB Output is correct
60 Correct 508 ms 96444 KB Output is correct
61 Correct 6 ms 33116 KB Output is correct
62 Correct 7 ms 33116 KB Output is correct
63 Correct 366 ms 87508 KB Output is correct
64 Correct 8 ms 33884 KB Output is correct
65 Correct 17 ms 38336 KB Output is correct
66 Correct 138 ms 70340 KB Output is correct
67 Correct 650 ms 102604 KB Output is correct
68 Correct 595 ms 102840 KB Output is correct
69 Correct 11 ms 36952 KB Output is correct
70 Correct 77 ms 63420 KB Output is correct
71 Correct 255 ms 98188 KB Output is correct
72 Correct 287 ms 98104 KB Output is correct
73 Correct 86 ms 53964 KB Output is correct
74 Correct 533 ms 90956 KB Output is correct
75 Correct 33 ms 41040 KB Output is correct
76 Correct 286 ms 98508 KB Output is correct
77 Correct 274 ms 98272 KB Output is correct
78 Correct 31 ms 41052 KB Output is correct
79 Correct 562 ms 97104 KB Output is correct
80 Correct 8 ms 33624 KB Output is correct
81 Correct 91 ms 61536 KB Output is correct
82 Correct 377 ms 98136 KB Output is correct
83 Correct 521 ms 90944 KB Output is correct
84 Correct 484 ms 90820 KB Output is correct
85 Correct 516 ms 90944 KB Output is correct
86 Correct 523 ms 97604 KB Output is correct
87 Correct 520 ms 96960 KB Output is correct