【题解】CF359B Permutation

【题解】CF359B Permutation

求一个长度为\(2n\)的序列，满足\(\Sigma |a_{2i}-a_{2i-1}|-|\Sigma a_{2i}-a_{2i-1}|=2k\)

这种带绝对值的题目套路就是把绝对值拆开。看看\(n=2\)时候的情况

\(\left[1,2,3,4\right]\)

\(|2-1|+|4-3|-|2-1+4-3|=0\)

\(swap(1,2) =>\)

\(|1-2|+|4-3|-|1-2+4-3|=2\)

也就是交换一组产生\(2\)的贡献，直接交换\(k\)组就好了。

#include<iostream>

#include<cstring>

#include<algorithm>

#include<cstdio>

#include<queue>

#include<bitset>

#include<vector>

#include<map>

#include<ctime>

#include<cstdlib>

#include<set>

#include<bitset>

#include<stack>

#include<list>

#include<cmath>

using namespace std;

#define RP(t,a,b) for(register int (t)=(a),edd_=(b);t<=edd_;++t)

#define DRP(t,a,b) for(register int (t)=(a),edd_=(b);t>=edd_;--t)

#define ERP(t,a) for(int t=head[a];t;t=e[t].nx)

#define Max(a,b) ((a)<(b)?(b):(a))

#define Min(a,b) ((a)<(b)?(a):(b))

#define TMP template<class ccf>

#define lef L,R,l,mid,pos<<1

#define rgt L,R,mid+1,r,pos<<1|1

#define midd register int mid=(l+r)>>1

#define chek if(R<l||r<L)return

#define all 1,n,1

#define pushup(x) seg[(x)]=seg[(x)<<1]+seg[(x)<<1|1]

typedef long long ll;

TMP inline ccf qr(ccf k){

    char c=getchar();

    ccf x=0;

    int q=1;

    while(c<48||c>57)

    q=c==45?-1:q,c=getchar();

    while(c>=48&&c<=57)

    x=x*10+c-48,c=getchar();

    if(q==-1)

    x=-x;

    return x;

}

const int maxn=5e4+15;

int data[maxn<<1];

int n,k;

int main(){

#ifndef ONLINE_JUDGE

    freopen("in.in","r",stdin);

    freopen("out.out","w",stdout);

#endif

    n=qr(1);

    k=qr(1);

    RP(t,1,n*2+1)

    data[t]=t;

    RP(t,1,k)

    swap(data[t<<1],data[(t<<1)-1]);

    RP(t,1,n*2-1)

    cout<<data[t]<<' ';

    cout<<data[n*2];

    return 0;

}