Codeforces 193D Two Segments (线段树)

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <vector>
#include <queue>
#include <map>
#include <set>
#include <algorithm>
#include <ctime>
#include <cstdlib>
#include <functional>
#pragma comment(linker,"/STACK:102400000,102400000")
using namespace std;

#define eps 1e-10
#define N 300030
#define B 20
#define M 3000020
#define inf 0x3f3f3f3f
#define LL long long
#define pii pair<int, int>
#define MP make_pair
#define fi first
#define se second
#define mod 1000000007
#define ls (i << 1)
#define rs (ls | 1)
#define md (ll + rr >> 1)
#define lson ll, md, ls
#define rson md + 1, rr, rs

int mi1[N << 2], mi2[N << 2], s1[N << 2], s2[N << 2], lazy[N << 2];

int n, a
, f
;

void build(int ll, int rr, int i) {
mi1[i] = 0, s1[i] = rr - ll + 1;
mi2[i] = inf, s2[i] = 0;
if(ll == rr) return;
build(lson);
build(rson);
}
LL ans;
int t;

void upd(int v, int i) {
mi1[i] += v;
mi2[i] += v;
lazy[i] += v;
}

void push_down(int i) {
if(lazy[i]) {
upd(lazy[i], ls);
upd(lazy[i], rs);
lazy[i] = 0;
}
}
void calc(int i, int x, int v) {
if(v == 0) return;
if(x < mi1[i]) {
mi2[i] = mi1[i], s2[i] = s1[i];
mi1[i] = x, s1[i] = v;
}
else if(x == mi1[i]) {
s1[i] += v;
}
else if(x < mi2[i]) {
mi2[i] = x, s2[i] = v;
}
else if(x == mi2[i]) {
s2[i] += v;
}
}
void push_up(int i) {
mi1[i] = mi1[ls], s1[i] = s1[ls];
mi2[i] = mi2[ls], s2[i] = s2[ls];
calc(i, mi1[rs], s1[rs]);
calc(i, mi2[rs], s2[rs]);
}
void update(int l, int r, int v, int ll, int rr, int i) {
if(ll == l && rr == r) {
upd(v, i);
return;
}
push_down(i);
if(r <= md) update(l, r, v, lson);
else if(l > md) update(l, r, v, rson);
else {
update(l, md, v, lson);
update(md + 1, r, v, rson);
}
push_up(i);
}

void query(int l, int r, int ll, int rr, int i) {
if(ll == l && rr == r) {
calc(t, mi1[i], s1[i]);
calc(t, mi2[i], s2[i]);
return;
}
push_down(i);
if(r <= md) query(l, r, lson);
else if(l > md) query(l, r, rson);
else {
query(l, md, lson);
query(md + 1, r, rson);
}
}
int main() {
scanf("%d", &n);
for(int i = 1; i <= n; ++i) {
scanf("%d", &a[i]);
f[a[i]] = i;
}
build(1, n, 1);
ans = 0;
t = (N << 2) - 1;
for(int i = 1; i <= n; ++i) {
int l = -1, r = -1;
if(f[i] > 1 && a[f[i] - 1] <= i) l = a[f[i] - 1];
if(f[i] < n && a[f[i] + 1] <= i) r = a[f[i] + 1];
if(l > r) swap(l, r);
if(r == -1) update(1, i, 1, 1, n, 1);
else if(l == -1) {
update(r + 1, i, 1, 1, n, 1);
}
else {
update(r + 1, i, 1, 1, n, 1);
update(1, l, -1, 1, n, 1);
}

mi1[t] = inf, mi2[t] = inf;
query(1, i, 1, n, 1);
if(mi1[t] == 1) ans += s1[t];
if(mi2[t] == 2) ans += s2[t];

}
printf("%lld\n", ans - n);
return 0;
}