Submission #395449

#	Time	Username	Problem	Language	Result	Execution time	Memory
395449		rocks03	Sorting (IOI15_sorting)	C++14	20 / 100	1077 ms	460 KiB

sorting

//#pragma GCC target("avx2")
//#pragma GCC optimization("O3")
//#pragma GCC optimization("unroll-loops")
#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define pii pair<int, int>
#define pll pair<ll, ll>
#define ff first
#define ss second
#define pb push_back
#define SZ(x) ((int)(x).size())
#define all(x) x.begin(), x.end()
#define rep(i, a, b) for(int i = (a); i < (b); i++)
#define per(i, a, b) for(int i = (a); i >= (b); i--)
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

int findSwapPairs(int N, int B[], int M, int X[], int Y[], int P[], int Q[]){
    int np[M], nq[M];
    vector<int> a, pos;
    set<int> st;
    auto swappa = [&](int i, int j){
        auto it = st.find(a[i]);
        if(it != st.end()) st.erase(it);
        it = st.find(a[j]);
        if(it != st.end()) st.erase(it);
        swap(pos[a[i]], pos[a[j]]);
        swap(a[i], a[j]);
        if(a[i] != i) st.insert(a[i]);
        if(a[j] != j) st.insert(a[j]);
    };
    auto random_sol = [&](){
        int ans = 0;
        while(SZ(st) && ans <= M){
            int i = X[ans], j = Y[ans];
            swappa(i, j);
            if(SZ(st) == 0){
                np[ans] = 0;
                nq[ans] = 0;
                ans++; break;
            }
            int x = rng() % N;
            auto it = st.lower_bound(x);
            if(it == st.end()) it--;
            x = *it;
            i = pos[x], j = x;
            np[ans] = i; nq[ans] = j;
            ans++;
            swappa(i, j);
        }
        return ans;
    };
    while(true){
        pos = a = vector<int>(N);
        rep(i, 0, N){
            a[i] = B[i];
            pos[a[i]] = i;
        }
        st.clear();
        rep(i, 0, N){
            if(a[i] != i) st.insert(i);
        }
        int ans = random_sol();
        if(ans > M) continue;
        rep(i, 0, N) a[i] = B[i];
        rep(i, 0, ans){
            swap(a[X[i]], a[Y[i]]);
            swap(a[np[i]], a[nq[i]]);
        }
        rep(i, 0, ans){
            if(a[i] != i){
                ans = -1; break;
            }
        }
        if(ans != -1){
            rep(i, 0, N){
                P[i] = np[i];
                Q[i] = nq[i];
            }
            return ans;
        }
    }
}

Compilation message (stderr)

sorting.cpp: In lambda function:
sorting.cpp:42:27: warning: conversion from 'std::mersenne_twister_engine<long unsigned int, 32, 624, 397, 31, 2567483615, 11, 4294967295, 7, 2636928640, 15, 4022730752, 18, 1812433253>::result_type' {aka 'long unsigned int'} to 'int' may change value [-Wconversion]
   42 |             int x = rng() % N;
      |                     ~~~~~~^~~

• Subtask 1: 8 / 8
• Subtask 2: 12 / 12
• Subtask 3: 0 / 16
• Subtask 4: 0 / 18
• Subtask 5: 0 / 20
• Subtask 6: 0 / 26