Submission #669718

#	Time	Username	Problem	Language	Result	Execution time	Memory
669718		victor_gao	Sorting (IOI15_sorting)	C++17	20 / 100	1096 ms	408 KiB

sorting

#include "sorting.h"
#include <bits/stdc++.h>
#define MAXN 200015
using namespace std;
int bk[MAXN],pos_bk[MAXN],pre[MAXN],pos_pre[MAXN];
int solve(int N,int n,int S[],int P[],int Q[],int X[],int Y[]){
    int now=0,cnt_same=0;
    for (int i=0;i<N;i++){
        bk[i]=i; pos_bk[i]=i;
        pre[i]=S[i];  pos_pre[S[i]]=i;
        if (pre[i]==i) cnt_same++;
    }
    for (int i=n-1;i>=0;i--){
        swap(bk[X[i]],bk[Y[i]]);
        pos_bk[bk[X[i]]]=X[i];
        pos_bk[bk[Y[i]]]=Y[i];
    }
    for (int i=0;i<n;i++){
        if (cnt_same==N) return i;
        if (pre[X[i]]==X[i]) cnt_same--;
        if (pre[Y[i]]==Y[i]) cnt_same--;
        swap(pre[X[i]],pre[Y[i]]);
        if (pre[X[i]]==X[i]) cnt_same++;
        if (pre[Y[i]]==Y[i]) cnt_same++;
        pos_pre[pre[X[i]]]=X[i];
        pos_pre[pre[Y[i]]]=Y[i];
        swap(bk[X[i]],bk[Y[i]]);
        pos_bk[bk[X[i]]]=X[i];
        pos_bk[bk[Y[i]]]=Y[i];
        now=i;
        while (now<N&&pos_pre[now]==pos_bk[now])
            now++;
        if (now>=N) continue;
        P[i]=pos_pre[now]; Q[i]=pos_bk[now];
        if (pre[P[i]]==P[i]) cnt_same--;
        if (pre[Q[i]]==Q[i]) cnt_same--;
        swap(pre[pos_pre[now]],pre[pos_bk[now]]);
        if (pre[P[i]]==P[i]) cnt_same++;
        if (pre[Q[i]]==Q[i]) cnt_same++;
        pos_pre[pre[pos_pre[now]]]=pos_pre[now];
        pos_pre[pre[pos_bk[now]]]=pos_bk[now];
    }
    bool flag=1;
    for (int i=0;i<N;i++){
        if (pre[i]!=i) flag=0;
    }
    if (flag) return n;
    else return 1e9;
}
int solve1(int N,int n,int S[],int P[],int Q[],int X[],int Y[]){
    for (int i=0;i<N;i++){
        bk[i]=i; pos_bk[i]=i;
        pre[i]=S[i];  pos_pre[S[i]]=i;
    }
    for (int i=n-1;i>=0;i--){
        swap(bk[X[i]],bk[Y[i]]);
        pos_bk[bk[X[i]]]=X[i];
        pos_bk[bk[Y[i]]]=Y[i];
    }
    int now=0;
    for (int i=0;i<n;i++){
        bool flag=1;
        for (int j=0;j<N;j++){
            if (pre[j]!=j){
                flag=0;
                break;
            } 
        }
        if (flag)
            return i;
        swap(pre[X[i]],pre[Y[i]]);
        pos_pre[pre[X[i]]]=X[i];
        pos_pre[pre[Y[i]]]=Y[i];
        swap(bk[X[i]],bk[Y[i]]);
        pos_bk[bk[X[i]]]=X[i];
        pos_bk[bk[Y[i]]]=Y[i];
        now=i;
        while (now<N&&pos_pre[now]==pos_bk[now])
            now++;
        if (now>=N) continue;
        P[i]=pos_pre[now]; Q[i]=pos_bk[now];
        swap(pre[pos_pre[now]],pre[pos_bk[now]]);
        pos_pre[pre[pos_pre[now]]]=pos_pre[now];
        pos_pre[pre[pos_bk[now]]]=pos_bk[now];
    }
    bool flag=1;
    for (int i=0;i<N;i++){
        if (pre[i]!=i) flag=0;
    }
    if (flag) return n;
    else return 1e9;
}
int findSwapPairs(int N, int S[], int M, int X[], int Y[], int P[], int Q[]) {
    /*
    int l=0,r=M;
    while (l<r){
        int mid=(l+r)>>1;
        if (solve(N,mid,S,P,Q,X,Y)<1e8) r=mid;
        else l=mid+1;
    }
    return solve(N,l,S,P,Q,X,Y);
    */
    int mn=1e9,pos;
    for (int i=0;i<M;i++){
        int need=solve1(N,i,S,P,Q,X,Y);
        if (need<1e8){
            if (mn>need){
                mn=need;
                pos=i;
            }
        }
    }
    return solve1(N,pos,S,P,Q,X,Y);
}

Compilation message (stderr)

sorting.cpp: In function 'int findSwapPairs(int, int*, int, int*, int*, int*, int*)':
sorting.cpp:113:18: warning: 'pos' may be used uninitialized in this function [-Wmaybe-uninitialized]
  113 |     return solve1(N,pos,S,P,Q,X,Y);
      |            ~~~~~~^~~~~~~~~~~~~~~~~

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