Educational Codeforces Round 30 D

Merge Sort

题意：给出归并排序的规则，构造一个长度为n的序列，使得序列按归并排序递归k次变为有序

思路：先构造一个有序序列，然后倒着模拟归并排序的递归过程，每次递归将有序变为无序

AC代码：

#include "iostream"
#include "iomanip"
#include "string.h"
#include "stack"
#include "queue"
#include "string"
#include "vector"
#include "set"
#include "map"
#include "algorithm"
#include "stdio.h"
#include "math.h"
#pragma comment(linker, "/STACK:102400000,102400000")
#define bug(x) cout<<x<<" "<<"UUUUU"<<endl;
#define mem(a,x) memset(a,x,sizeof(a))
#define step(x) fixed<< setprecision(x)<<
#define mp(x,y) make_pair(x,y)
#define pb(x) push_back(x)
#define ll long long
#define endl ("
")
#define ft first
#define sd second
#define lrt (rt<<1)
#define rrt (rt<<1|1)
using namespace std;
const ll mod=1e9+7;
const ll INF = 1e18+1LL;
const int inf = 1e9+1e8;
const double PI=acos(-1.0);
const int N=1e5+100;

int n,k,a[N],f[N];

void dfs(int l, int r){
    if(k<=1 || r<=l+1) return;
    k-=2;
    int mid=l+r>>1;
    swap(a[mid-1],a[mid]);
    dfs(l, mid);
    dfs(mid, r);
}

int main(){
    ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
    cin>>n>>k;
    if((k&1)==0 || k>=2*n){
        cout<<-1;
        return 0;
    }
    int d=log2(n)+1;
    for(int i=1; i<=n; ++i) a[i]=i;
    dfs(1, n+1);
    for(int i=1; i<=n; ++i) cout<<a[i]<<" ";
    return 0;
}