Problem:
Score : 400 points

Problem Statement

One day, Snuke was given a permutation of length N, a_1, a_2, ..., a_N, from his friend.

Find the following:

Constraints

1 ≦ N ≦ 200,000

(a_1, a_2, ..., a_N) is a permutation of (1, 2, ..., N).

Input

The input is given from Standard Input in the following format:

N
a_1 a_2 ... a_N

Output

Print the answer.

Note that the answer may not fit into a 32-bit integer.

Sample Input 1

3
2 1 3

Sample Output 1

9

Sample Input 2

4
1 3 2 4

Sample Output 2

19

Sample Input 3

8
5 4 8 1 2 6 7 3

Sample Output 3

85

Solution in C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>

using namespace std;

const int MAX = 200005;
int N;

int X[MAX];
int Y[MAX];

typedef long long ll;

void slove() {
    for (int i = 0; i < N; ++i) {
        Y[X[i]] = i;
    }

    ll ans = 0;

    int l;
    int r;

    set<int> S;
    S.insert(-1);
    S.insert(N);

    for (int i = 1; i <= N; ++i) {
        int p = Y[i];

        //auto il = S.lower_bound(p);
        auto iu = S.upper_bound(p); // ok
        auto il = iu;
        il--;

        //cout << i << " " << p << endl;
        //cout << "il: " << *il << endl;
        //cout << "iu: " << *iu << endl;

        l = p - *il;
        r = *iu - p;

        //cout << l << endl;
        //cout << r << endl;
        //cout << "---" << endl;

        S.insert(p);

        ans += ((ll) l) * ((ll) r) * ((ll) i);
    }

    cout << ans << endl;
}

int main(int argc, char* argv[]) {
    cin >> N;

    for (int i = 0; i < N; ++i) {
        cin >> X[i];
    }

    slove();

    return 0;
}