Submission #1270582

#	Time	Username	Problem	Language	Result	Execution time	Memory
1270582		nathan4690	Tug of War (BOI15_tug)	C++20	100 / 100	861 ms	6344 KiB

tug

#include <bits/stdc++.h>
#define ll long long
#define ld long double
#define f1(i,n) for(int i=1;i<=n;i++)
#define __file_name ""
#define pii pair<int,int>
using namespace std;
const ll maxn = 1e6+5, inf=1e18;

struct DSU{
    int n;
    vector<int> p,sz,e;
    DSU(){};
    DSU(int n): n(n), p(n+1, 0), sz(n+1, 1), e(n+1, 0){
        f1(i,n) p[i] = i;
    }
    int find_set(int u){
        return (u == p[u] ? u : p[u] = find_set(p[u]));
    }
    void union_set(int u, int v){
        u = find_set(u);
        v = find_set(v);
        e[u]++;
        if(u == v) return;
        if(sz[u] < sz[v]) swap(u, v);
        p[v] = u;
        sz[u] += sz[v];
        e[u] += e[v];
    }
};

int n, k, deg[maxn], le, ri, w0, w1, root, wei[maxn];
bool del[maxn], used[maxn];
vector<pair<int,int>> G[maxn];
priority_queue<pii, vector<pii>, greater<pii>> pq;
bitset<600001> bit;

void dfs(int u, int col){
    del[u] = 1;
    for(pair<int,int> e: G[u]){
        int c = e.first, w = wei[e.second];
        if((!used[e.second]) && (c == root || !del[c])){
            if(col) w1 += w;
            else w0 += w;
            used[e.second] = 1;
            if(!del[c]) dfs(c, col ^ 1);
            return;
        }
    }
}

int main(){
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);

    if(fopen(__file_name ".inp", "r")){
        freopen(__file_name ".inp","r",stdin);
        freopen(__file_name ".out","w",stdout);
    }
    // code here
    cin >> n >> k;
    DSU dsu(2*n);
    int sum = 0;
    f1(i,2*n){
        int l, r, s; cin >> l >> r >> s;
        dsu.union_set(l, n + r);
        G[l].push_back({n + r, i});
        G[n + r].push_back({l, i});
        wei[i] = s;
//        cout << l << ' ' << n + r << ' ' << s << '\n';
        deg[l]++; deg[n + r]++;
        sum += s;
    }
    f1(i,2*n){
        pq.push({deg[i], i});
        if(dsu.find_set(i) == i){
            if(dsu.e[i] != dsu.sz[i]){
                cout << "NO\n";
                return 0;
            }
        }
    }
    while(!pq.empty()){
        int dg = pq.top().first, u = pq.top().second;
        pq.pop();
        if(dg != deg[u]) continue;
        if(dg > 1) continue;
        del[u] = true;
        for(pair<int,int> e: G[u]){
            int c = e.first, w = wei[e.second];
            if(del[c]) continue;
            if(c > n) ri += w;
            else le += w;
            deg[c]--;
            pq.push({deg[c], c});
        }
    }
    bit.set(le, 1);
    f1(i, 2*n){
        if(!del[i]){
            root = i;
            w0 = w1 = 0;
            dfs(i, 0);
//            cout << w0 << ' ' << w1 << '\n';
            bit = (bit << w0) | (bit << w1);
        }
    }
    for(int i=min(sum, sum / 2 + k + 1); i>=max(0, sum / 2 - k);i--){
        if(bit.test(i)){
            int v = sum - i;
//            cout << i << ' ' << v << '\n';
            if(abs(v - i) <= k) return cout << "YES\n", 0;
        }
    }
    cout << "NO\n";
    return 0;
}

Compilation message (stderr)

tug.cpp: In function 'int main()':
tug.cpp:56:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   56 |         freopen(__file_name ".inp","r",stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
tug.cpp:57:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   57 |         freopen(__file_name ".out","w",stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 18 / 18
• Subtask 2: 30 / 30
• Subtask 3: 23 / 23
• Subtask 4: 29 / 29