Submission #958911

#	Time	Username	Problem	Language	Result	Execution time	Memory
958911		TAhmed33	Fancy Fence (CEOI20_fancyfence)	C++98	100 / 100	32 ms	17748 KiB

fancyfence

#include <bits/stdc++.h>
using namespace std;
const int MOD = 1e9 + 7;
const int TWOINV = 5e8 + 4;
const int MAXN = 1e5 + 25;
int add (int a, int b) {
    a += b; if (a >= MOD) a -= MOD;
    return a;
}
int sub (int a, int b) {
    a -= b; if (a < 0) a += MOD;
    return a;
}
int mul (int a, int b) {
    return (a * 1ll * b) % MOD;
}
int h[MAXN], w[MAXN], n;
int nxt[MAXN], prv[MAXN], sze[MAXN];
vector <int> adj[MAXN];
bool comp (int x, int y) {
    return h[x] == h[y] ? x < y : h[x] < h[y];
}
int ans;
void dfs (int pos) {
    sze[pos] = w[pos];
    int x = mul(h[pos], mul(h[pos] + 1, TWOINV));
    for (auto j : adj[pos]) {
        dfs(j);
        ans = add(ans, mul(sze[j], mul(sze[pos], x)));
        sze[pos] = add(sze[pos], sze[j]);
    }
}
int main () {
    ios::sync_with_stdio(0); cin.tie(0);
    cin >> n; memset(nxt, -1, sizeof(nxt)); memset(prv, -1, sizeof(prv));
    for (int i = 1; i <= n; i++) cin >> h[i];
    for (int i = 1; i <= n; i++) cin >> w[i];
    for (int i = 1; i <= n; i++) {
        int x = w[i], y = h[i];
        x = mul(x, mul(x + 1, TWOINV));
        y = mul(y, mul(y + 1, TWOINV));
        ans = add(ans, mul(x, y));
    }
    stack <int> cur;
    for (int i = 1; i <= n; i++) {
        while (!cur.empty() && comp(i, cur.top())) {
            nxt[cur.top()] = i;
            cur.pop();
        }
        cur.push(i);
    }
    while (!cur.empty()) cur.pop();
    for (int i = n; i >= 1; i--) {
        while (!cur.empty() && comp(i, cur.top())) {
            prv[cur.top()] = i;
            cur.pop();
        }
        cur.push(i);
    }
    while (!cur.empty()) cur.pop();
    int root = -1;
    for (int i = 1; i <= n; i++) {
        if (nxt[i] == -1 && prv[i] == -1) {
            root = i;
            continue;
        }
        if (nxt[i] == -1) {
            adj[prv[i]].push_back(i);
        } else if (prv[i] == -1) {
            adj[nxt[i]].push_back(i);
        } else if (!comp(nxt[i], prv[i])) {
            adj[nxt[i]].push_back(i);
        } else {
            adj[prv[i]].push_back(i);
        }
    }
    dfs(root);
    cout << ans << '\n';
}

• Subtask 1: 0 / 0
• Subtask 2: 12 / 12
• Subtask 3: 13 / 13
• Subtask 4: 15 / 15
• Subtask 5: 15 / 15
• Subtask 6: 18 / 18
• Subtask 7: 27 / 27