https://www.luogu.com.cn/problem/P3515
p i = max j = 1 n ( a j + ∣ i − j ∣ ) − a i p_i=\max_{j=1}^n(a_j+\sqrt {|i-j|})-a_i pi=maxj=1n(aj+∣i−j∣)−ai, p p p 之间独立,直接拆绝对值,到时候reverse再做一遍即可。
拆绝对值后,显然具有决策单调性,因为 i − j \sqrt {i-j} i−j 以 i i i 为自变量,求导后为减函数。然后我们采用二分队列优化。
此题关键:
- 直接暴力表示,然后拆绝对值
- 看出来满足决策单调性(去根号影响!)
#include<bits/stdc++.h>
using namespace std;
#ifdef LOCAL#define debug(...) fprintf(stdout, ##__VA_ARGS__)
#else#define debug(...) void(0)
#endif
#define int long long
inline int read(){int x=0,f=1;char ch=getchar();
while(ch<'0'||ch>'9'){if(ch=='-')f=-1;
ch=getchar();}while(ch>='0'&&ch<='9'){x=(x<<1)+
(x<<3)+(ch^48);ch=getchar();}return x*f;}
#define Z(x) (x)*(x)
#define pb push_back
#define fi first
#define se second
//#define M
//#define mo
#define N 500010
struct node {int x, l, r;
};
int n, m, i, j, k, T;
double a[N];
int p[N], p1[N], p2[N];
int l, r, mid;
deque<node>q; double calc(int j, int i) {return a[j]+sqrt((double)(i-j));
}void work(int *p) {while(!q.empty()) q.pop_back(); for(i=1; i<=n; ++i) {if(!q.empty()) {auto t = q.front(); q.pop_front(); t.l=i; if(t.l<=t.r) q.push_front(t); }node t; t.r=n; t.l=n+1; t.x=i; if(i==1) t.l=i; while(!q.empty() && calc(i, q.back().l) >= calc(q.back().x, q.back().l)) t.l=q.back().l, q.pop_back(); if(!q.empty() && calc(i, q.back().r)>=calc(q.back().x, q.back().r)) {l=q.back().l; r=q.back().r; k=q.back().x; while(l<r) {mid=(l+r)>>1; if(calc(i, mid)>=calc(k, mid)) r=mid; else l=mid+1; }t.l=l; auto t2=q.back(); q.pop_back(); t2.r=l-1; q.push_back(t2); }if(t.l<=t.r) q.push_back(t); if(!q.empty()) {p[i]=(int)ceil(calc(q.front().x, i));
// debug("%d -> %d %d\n", q.front().x, i, p[i]); }
// debug("> %d")}
}signed main()
{#ifdef LOCALfreopen("in.txt", "r", stdin);freopen("out.txt", "w", stdout);#endif
// srand(time(NULL));
// T=read();
// while(T--) {
//
// }n=read(); for(i=1; i<=n; ++i) a[i]=read(); work(p1); reverse(a+1, a+n+1); work(p2); reverse(p2+1, p2+n+1); reverse(a+1, a+n+1); for(i=1; i<=n; ++i) p[i]=max(max(p1[i], p2[i]), 0ll)-(int)a[i]; for(i=1; i<=n; ++i) printf("%lld\n", p[i]); return 0;
}