Submission #553830

#	Time	Username	Problem	Language	Result	Execution time	Memory
553830		Awerar	The Xana coup (BOI21_xanadu)	C++14	100 / 100	253 ms	50580 KiB

xanadu

#include <iostream>
#include <vector>
#include <string>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <limits.h>
#include <math.h>
#include <chrono>
#include <queue>
#include <stack>
#include <algorithm>

using namespace std;

#pragma GCC target ("avx2")
#pragma GCC optimization ("O3")
#pragma GCC optimization ("unroll-loops")

#define ll long long
#define vi vector<ll>
#define vvi vector<vi>
#define p2 pair<ll, ll>
#define p3 tuple<ll,ll,ll>
#define p4 vi
#define ip3 tuple<int,int,int>
#define ip4 tuple<int,int,int,int>
#define vp2 vector<p2>
#define vp3 vector<p3>
#define inf 2e9
#define linf 1e17

#define read(a) cin >> a
#define write(a) cout << (a) << "\n"
#define dread(type, a) type a; cin >> a
#define dread2(type, a, b) dread(type, a); dread(type, b)
#define dread3(type, a, b, c) dread2(type, a, b); dread(type, c)
#define dread4(type, a, b, c, d) dread3(type, a, b, c); dread(type, d)
#define dread5(type, a, b, c, d, e) dread4(type, a, b, c, d); dread(type, e)
#ifdef _DEBUG
#define deb __debugbreak();
#else
#define deb ;
#endif

#define rep(i, high) for (ll i = 0; i < high; i++)
#define repp(i, low, high) for (ll i = low; i < high; i++)
#define repe(i, container) for (auto& i : container)
#define per(i, high) for (ll i = high; i >= 0; i--)

#define readpush(type,vect) type temp; read(temp); vect.push_back(temp);
#define readvector(type, name, size) vector<type> name(size); rep(i,size) {dread(type,temp); name[i]=temp;}
#define readinsert(type,a) {type temp; read(temp); a.insert(temp);}
#define all(a) begin(a),end(a)
#define setcontains(set, x) (set.find(x) != set.end())
#define stringcontains(str, x) (str.find(x) != string::npos)
#define within(a, b, c, d) (a >= 0 && a < b && c >= 0 && c < d)

#define ceildiv(x,y) ((x + y - 1) / y)
#define fract(a) (a-floor(a))
#define sign(a) ((a>0) ? 1 : -1)

auto Start = chrono::high_resolution_clock::now();

inline void fast()
{
    ios::sync_with_stdio(false);
    cin.tie(NULL); cout.tie(NULL);
}

vector<unordered_set<int>> children;
vector<int> parent;
vector<bool> is_on;
int n;

void dfs(int n, int par) {
    parent[n] = par;
    children[n].erase(par);

    for(int child : children[n]) dfs(child, n);
}

vector<vector<ll*>> dp_table;
long long dp(int n, bool parent_switched, bool need_switch) {
    ll*& ref = dp_table[n][parent_switched * 2 + need_switch];
    if(ref != NULL) return *ref;

    bool odd = is_on[n] ^ parent_switched ^ need_switch;

    long long result = 0;
    int flips = 0;
    long long worst_flip = -1, worst_not_flip = -1;
    for(int c : children[n]) {
        long long flip = dp(c, need_switch, true);
        long long no_flip = dp(c, need_switch, false);

        result += min(flip, no_flip);
        if(flip < no_flip) {
            flips++;
            if(no_flip - flip < worst_flip || worst_flip == -1) {
                worst_flip = no_flip - flip;
            }
        } else {
            if(flip - no_flip < worst_not_flip || worst_not_flip == -1) {
                worst_not_flip = flip - no_flip;
            }
        }
    }

    if((flips % 2 == 1) != odd) {
        if(worst_flip == -1 && worst_not_flip == -1) return inf;
        else if((worst_flip == -1) ^ (worst_not_flip == -1)) result += max(worst_not_flip, worst_flip);
        else result += min(worst_not_flip, worst_flip);
    }

    ref = new ll(result + need_switch);
    return *ref;
}

int main() {
    //fast();
    
    cin >> n;
    is_on.resize(n);
    children.resize(n);
    parent.resize(n);
    dp_table.resize(n, vector<ll*>(4, NULL));

    for(int i = 0; i < n - 1; i++) {
        dread2(int, a, b);
        a--;
        b--;

        children[a].insert(b);
        children[b].insert(a);
    }

    dfs(0, -1);

    rep(i, n) {
        char q;
        cin >> q;
        is_on[i] = q == '1';
    }

    long long result = min(dp(0, false, false), dp(0, false, true));
    if(result < n) write(result);
    else write("impossible");
}

/*
5
1 2
1 3
2 4
2 5
0 1 0 1 1

5
1 2
2 3
3 4
4 5
0 1 1 1 1


*/

Compilation message (stderr)

xanadu.cpp:18: warning: ignoring '#pragma GCC optimization' [-Wunknown-pragmas]
   18 | #pragma GCC optimization ("O3")
      | 
xanadu.cpp:19: warning: ignoring '#pragma GCC optimization' [-Wunknown-pragmas]
   19 | #pragma GCC optimization ("unroll-loops")
      |

• Subtask 1: 5 / 5
• Subtask 2: 15 / 15
• Subtask 3: 10 / 10
• Subtask 4: 40 / 40
• Subtask 5: 30 / 30