HackerEarth Counting the number of intervals solution

#include <bits/stdc++.h>
using namespace std;

#define ms(s, n) memset(s, n, sizeof(s))
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define FORd(i, a, b) for (int i = (a) - 1; i >= (b); --i)
#define FORall(it, a) for (__typeof((a).begin()) it = (a).begin(); it != (a).end(); it++)
#define sz(a) int((a).size())
#define present(t, x) (t.find(x) != t.end())
#define all(a) (a).begin(), (a).end()
#define uni(a) (a).erase(unique(all(a)), (a).end())
#define pb push_back
#define pf push_front
#define mp make_pair
#define fi first
#define se second
#define prec(n) fixed<<setprecision(n)
#define bit(n, i) (((n) >> (i)) & 1)
#define bitcount(n) __builtin_popcountll(n)
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<int, int> pi;
typedef vector<int> vi;
typedef vector<pi> vii;
const int MOD = (int) 1e9 + 7;
const int FFTMOD = 119 << 23 | 1;
const int INF = (int) 1e9 + 23111992;
const ll LINF = (ll) 1e18 + 23111992;
const ld PI = acos((ld) -1);
const ld EPS = 1e-9;
inline ll gcd(ll a, ll b) {ll r; while (b) {r = a % b; a = b; b = r;} return a;}
inline ll lcm(ll a, ll b) {return a / gcd(a, b) * b;}
inline ll fpow(ll n, ll k, int p = MOD) {ll r = 1; for (; k; k >>= 1) {if (k & 1) r = r * n % p; n = n * n % p;} return r;}
template<class T> inline int chkmin(T& a, const T& val) {return val < a ? a = val, 1 : 0;}
template<class T> inline int chkmax(T& a, const T& val) {return a < val ? a = val, 1 : 0;}
inline ull isqrt(ull k) {ull r = sqrt(k) + 1; while (r * r > k) r--; return r;}
inline ll icbrt(ll k) {ll r = cbrt(k) + 1; while (r * r * r > k) r--; return r;}
inline void addmod(int& a, int val, int p = MOD) {if ((a = (a + val)) >= p) a -= p;}
inline void submod(int& a, int val, int p = MOD) {if ((a = (a - val)) < 0) a += p;}
inline int mult(int a, int b, int p = MOD) {return (ll) a * b % p;}
inline int inv(int a, int p = MOD) {return fpow(a, p - 2, p);}
inline int sign(ld x) {return x < -EPS ? -1 : x > +EPS;}
inline int sign(ld x, ld y) {return sign(x - y);}
mt19937 mt(chrono::high_resolution_clock::now().time_since_epoch().count());
inline int myrand() {return abs((int) mt());}
#define db(x) cerr << #x << " = " << (x) << " ";
#define endln cerr << "n";

const int maxn = 5e5 + 5;
int n;
long long k;
long long a[maxn];
int l[maxn];
int r[maxn];
vii g[maxn];

int fen[maxn];
void upd(int p, int val) {
    p++;
    for (; p < maxn; p += p & -p) {
        fen[p] += val;
    }
}
int query(int p) {
    p++;
    int res = 0;
    for (; p > 0; p -= p & -p) {
        res += fen[p];
    }
    return res;
}

void chemthan() {
    cin >> n >> k;
    assert(1 <= n && n <= 5e5);
    assert(1 <= k && k <= 1e18);
    vector<long long> dc;
    FOR(i, 0, n) {
        cin >> a[i];
        assert(1 <= a[i] && a[i] <= 1e18);
        dc.pb(a[i]);
    }
    sort(all(dc)), uni(dc);
    FOR(i, 0, n) l[i] = r[i] = i;
    FOR(i, 1, n) {
        int ptr = i;
        while (ptr && a[i] < a[ptr - 1]) ptr = l[ptr - 1];
        l[i] = ptr;
    }
    FORd(i, n - 1, 0) {
        int ptr = i;
        while (ptr + 1 < n && a[i] <= a[ptr + 1]) ptr = r[ptr + 1];
        r[i] = ptr;
    }
    FOR(i, 0, n) {
        if (i - l[i] <= r[i] - i) {
            FOR(j, l[i], i + 1) {
                int d = upper_bound(all(dc), k - a[i] - a[j]) - dc.begin() - 1;
                g[r[i]].pb(mp(d, 1));
                if (i) {
                    g[i - 1].pb(mp(d, -1));
                }
            }
        }
        else {
            FOR(j, i, r[i] + 1) {
                int d = upper_bound(all(dc), k - a[i] - a[j]) - dc.begin() - 1;
                g[i].pb(mp(d, 1));
                if (l[i]) {
                    g[l[i] - 1].pb(mp(d, -1));
                }
            }
        }
    }
    long long res = 0;
    FOR(i, 0, n) {
        int k = lower_bound(all(dc), a[i]) - dc.begin();
        upd(k, 1);
        for (pi ev : g[i]) {
            res += query(ev.fi) * ev.se;
        }
    }
    cout << res << "n";
}

int main(int argc, char* argv[]) {
    ios_base::sync_with_stdio(0), cin.tie(0);
    if (argc > 1) {
        assert(freopen(argv[1], "r", stdin));
    }
    if (argc > 2) {
        assert(freopen(argv[2], "wb", stdout));
    }
    chemthan();
    cerr << "nTime elapsed: " << 1000 * clock() / CLOCKS_PER_SEC << "msn";
    return 0;
}