1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
|
using namespace std;
#define forl(i, l, r) for (int i = l; i <= r; i++)
#define forr(i, r, l) for (int i = r; i >= l; i--)
#define for1(i, n) for (int i = 1; i <= n; i++)
#define fro1(i, n) for (int i = 1; i <= n; i++)
#define for0(i, n) for (int i = 0; i < n; i++)
#define fro0(i, n) for (int i = 0; i < n; i++)
#define meminf(a) memset(a, inf, sizeof(a))
#define mem_1(a) memset(a, -1, sizeof(a))
#define mem0(a) memset(a, 0, sizeof(a))
#define memcp(a,b) memcpy(a,b,sizeof(b))
#define oper(type) bool operator <(const type y)const
#define mp make_pair
#define pu_b push_back
#define pu_f push_front
#define po_b pop_back
#define po_f pop_front
#define fi first
#define se second
#define whiel while
#define retrun return
typedef pair<long long, long long> pll;
typedef vector<long long> vll;
typedef pair<int, int> pii;
typedef unsigned long long ull;
typedef vector<int> vii;
typedef long double db;
typedef long long ll;
typedef int itn;
int (int &a,int &b,int &c,int &d){return scanf("%d%d%d%d",&a,&b,&c,&d);}
int (int &a,int &b,int &c){return scanf("%d%d%d",&a,&b,&c);}
int (int &a,int &b){return scanf("%d%d",&a,&b);}
int (ll &a){return scanf("%lld",&a);}
int (int &a){return scanf("%d",&a);}
int in(char *s){return scanf("%s",s);}
int in(char &s){return scanf("%c",&s);}
int in(db &a){return scanf("%Lf",&a);}
void out(int a){printf("%d",a);}
void outln(int a){printf("%dn",a);}
void out(ll a){printf("%lld",a);}
void outln(ll a){printf("%lldn",a);}
const db pi = acos((db)-1);
const ll inf =0x3f3f3f3f;
const db eps = 1e-8;
const int N = 2.1e5;
const ll mod = 1e9+7;
int sign(db a) { return a < -eps ? -1 : a > eps;}
int db_cmp(db a, db b){ return sign(a-b); }
struct da{
int a,r,pre,i;
da(int _a,int _r,int _p,ll _i){
a=_a;
r=_r;
pre=_p;
i=_i;
}
da(){}
};
stack<da>sta;
ll fun(itn a,int l,int r){
return (r-l+1ll)*(l+r)/2%mod*a%mod;
}
int a[N];
int main() {
itn n;
ll ans=0;
in(n);
for1(i,n){
in(a[i]);
}
for(int i=n;i>0;i--){
ll r=n;
whiel(sta.size()){
da tmp=sta.top();
if(tmp.a<=a[i]){
sta.pop();
}else{
ll p=(tmp.a*1ll*tmp.i-tmp.a+a[i]-a[i]*1ll*i)/(tmp.a-a[i]);
if(p>=tmp.r){
sta.pop();
}else{
r=p;
break;
}
}
}
assert(r<=n);
int pre=0;
if(sta.size()){
da tmp=sta.top();
pre=tmp.pre;
pre=(pre+fun(tmp.a,r-tmp.i+2,tmp.r-tmp.i+1))%mod;
}
sta.push(da(a[i],r,pre,i));
ans=(ans+pre+fun(a[i],1,r-i+1))%mod;
}
outln(ans);
return 0;
}
|
近期评论