再卖菜

csp2018.9第4题

用差分约束求差的最小值，然后有一些转化，比如前缀和
换成>=，跑最长路
a1*2≤x1+x2≤a1*2+1

d[2]-d[0]>=a1*2
d[0]-d[2]>=-a1*2-1

a2*3<=x1+x2+x3<=a2*3+2

.
.
.

an-1*2<=xn-1+xn<=an*2+1
x1>=1
x2>=1
x3>=1

#include<iostream>
#include<cstdio>
#include<queue>
#include<algorithm>
#include<cmath>
#include<ctime>
#include<set>
#include<map>
#include<stack>
#include<cstring>
#define inf 2147483647
#define ls rt<<1
#define rs rt<<1|1
#define lson ls,nl,mid,l,r
#define rson rs,mid+1,nr,l,r
#define N 100010
#define For(i,a,b) for(int i=a;i<=b;i++)
#define p(a) putchar(a)
#define g() getchar()

using namespace std;
int n ,a[310],d[310],x;
queue<int>q;
bool vis[1000010];
struct node{
    int v;
    int n;
    node *next;
}*e[100010];
void in(int &x){
    int y=1;
    char c=g();x=0;
    while(c<'0'||c>'9'){
        if(c=='-')y=-1;
        c=g();
    }
    while(c<='9'&&c>='0'){
        x=(x<<1)+(x<<3)+c-'0';c=g();
    }
    x*=y;
}
void o(int x){
    if(x<0){
        p('-');
        x=-x;
    }
    if(x>9)o(x/10);
    p(x%10+'0');
}

void push(int x,int y,int v){
    node *p;
    p=new node();
    p->n=y;
    p->v=v;
    if(e[x]==NULL)
        e[x]=p;
    else{
        p->next=e[x]->next;
        e[x]->next=p;
    }
}

void spfa(){
    For(i,1,n)d[i]=-6876868;
    q.push(0);
    while(q.size()>0){
        x=q.front();
        vis[x]=true;
        for(node *i=e[x];i!=NULL;i=i->next)
            if(d[i->n]<d[x]+i->v){
                d[i->n]=d[x]+i->v;
                if(!vis[i->n]){
                     q.push(i->n);
                vis[i->n]=true;
                }
            }
        vis[x]=false;
        q.pop();
    }
}

int main(){
    in(n);
    For(i,1,n)in(a[i]);
    
    push(0,2,a[1]*2);
    push(2,0,-a[1]*2-1);
    push(n-2,n,a[n]*2);
    push(n,n-2,-a[n]*2-1);
    
    
    For(i,2,n-1){
        push(i+1,i-2,-a[i]*3-2);
        push(i-2,i+1,a[i]*3);
    }
    For(i,1,n)
    push(i-1,i,1);
    spfa();
    For(i,1,n){
        o(d[i]-d[i-1]);p(' ');
    }
    return 0;
}