浅谈笛卡尔树+小A的柱状图

题目链接

题意：


题解：

图片来源

void build(int n) {
    top = 0;
    for(int i = 0; i < n; i++) {
        int k = top;
        while (k > 0 && a[st[k]] > a[i]) k--;
        if (k) rs[st[k]] = i;
        if (k < top) ls[i] = st[k + 1];
        st[++k] = i; 
        top = k;
    }
}

AC代码

/*
    Author : zzugzx
    Lang : C++
    Blog : blog.csdn.net/qq_43756519
*/
#include<bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define all(x) (x).begin(), (x).end()
#define endl '\n'
#define SZ(x) (int)x.size()
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int mod = 1e9 + 7;
//const int mod = 998244353;
const double eps = 1e-6;
const double PI = acos(-1.0);
const int maxn = 1e6 + 10;
const int N = 200 + 5;
const ll inf = 0x3f3f3f3f;
const int dir[][2]={{0, 1}, {1, 0}, {0, -1}, {-1, 0}, {1, 1}, {1, -1}, {-1, 1}, {-1, -1}};
int ls[maxn], rs[maxn], st[maxn], top;
ll h[maxn], a[maxn];
void build(int n) {
    top = 0;
    for(int i = 0; i < n; i++) {
        int k = top;
        while (k > 0 && h[st[k]] > h[i]) k--;
        if (k) rs[st[k]] = i;
        if (k < top) ls[i] = st[k + 1];
        st[++k] = i; 
        top = k;
    }
}
ll ans = 0;
int dfs(int x) {
    if (!x) return 0;
    ll sz = a[x];
    sz += dfs(ls[x]);
    sz += dfs(rs[x]);
    ans = max(ans, sz * h[x]);
    return sz;
}
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);
//  freopen("in.txt", "r", stdin);
//  freopen("out.txt", "w", stdout);
    int n;
    cin >> n;
    for (int i = 0; i < n; i++)
        cin >> a[i];
    for (int i = 0; i < n; i++)
        cin >> h[i];
    build(n);
    dfs(st[1]);
    cout << ans;
    return 0;
}