Submission #623706

#	Time	Username	Problem	Language	Result	Execution time	Memory
623706		Joshc	Tug of War (BOI15_tug)	C++11	100 / 100	2153 ms	10344 KiB

tug

#include <bits/stdc++.h>
using namespace std;
 
#define pii pair<int, int>
#define mp make_pair
#define f first
#define s second
 
multiset<pii> edges[60005];
bitset<1200001> pos;
int bal;
 
void dfs(int x, int c) {
    if (!edges[x].empty()) {
        pii cur = *edges[x].begin();
        edges[x].clear();
        edges[cur.f].erase(edges[cur.f].find(mp(x, cur.s)));
        bal += c*cur.s;
        dfs(cur.f, -c);
    }
}
 
int main() {
    int n, k, x, y, z, balance = 600000;
    scanf("%d%d", &n, &k);
    for (int i=1; i<=2*n; i++) {
        scanf("%d%d%d", &x, &y, &z);
        y += n;
        edges[x].insert(mp(y, z));
        edges[y].insert(mp(x, z));
    }
    vector<int> forced;
    for (int i=1; i<=2*n; i++) {
        if (edges[i].empty()) {
            printf("NO\n");
            return 0;
        }
        if (edges[i].size() == 1) forced.push_back(i);
    }
    while (!forced.empty()) {
        int cur = forced.back();
        forced.pop_back();
        pii x = *edges[cur].begin();
        edges[cur].clear();
        if (cur <= n) balance += x.s;
        else balance -= x.s;
        edges[x.f].erase(edges[x.f].find(mp(cur, x.s)));
        if (edges[x.f].size() == 1) forced.push_back(x.f);
    }
    pos.set(balance);
    for (int i=1; i<=2*n; i++) {
        if (!edges[i].empty()) {
            pii cur = *edges[i].begin();
            edges[i].erase(edges[i].find(cur));
            edges[cur.f].erase(edges[cur.f].find(mp(i, cur.s)));
            bal = cur.s;
            dfs(i, -1);
            //printf("Test: %d\n", bal);
            bal = abs(bal);
            pos = (pos << bal) | (pos >> bal);
        }
    }
    for (int i=-k; i<=k; i++) {
        if (0 <= 600000+i && 600000+i < 1200001 && pos[600000+i]) {
            printf("YES\n");
            return 0;
        }
    }
    printf("NO\n");
}

Compilation message (stderr)

tug.cpp: In function 'int main()':
tug.cpp:25:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   25 |     scanf("%d%d", &n, &k);
      |     ~~~~~^~~~~~~~~~~~~~~~
tug.cpp:27:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   27 |         scanf("%d%d%d", &x, &y, &z);
      |         ~~~~~^~~~~~~~~~~~~~~~~~~~~~

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