[hdu1506 Largest Rectangle in a Histogram]笛卡尔树

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#pragma comment(linker, "/STACK:10240000")
#include <map>
#include <set>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <vector>
#include <cstdio>
#include <string>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;

#define X                   first
#define Y                   second
#define pb                  push_back
#define mp                  make_pair
#define all(a)              (a).begin(), (a).end()
#define fillchar(a, x)      memset(a, x, sizeof(a))
#define copy(a, b)          memcpy(a, b, sizeof(a))

typedef long long ll;
typedef pair<int, int> pii;
typedef unsigned long long ull;

//#ifndef ONLINE_JUDGE
void RI(vector<int>&a,int n){a.resize(n);for(int i=0;i<n;i++)scanf("%d",&a[i]);}
void RI(){}void RI(int&X){scanf("%d",&X);}template<typename...R>
void RI(int&f,R&...r){RI(f);RI(r...);}void RI(int*p,int*q){int d=p<q?1:-1;
while(p!=q){scanf("%d",p);p+=d;}}void print(){cout<<endl;}template<typename T>
void print(const T t){cout<<t<<endl;}template<typename F,typename...R>
void print(const F f,const R...r){cout<<f<<", ";print(r...);}template<typename T>
void print(T*p, T*q){int d=p<q?1:-1;while(p!=q){cout<<*p<<", ";p+=d;}cout<<endl;}
//#endif
template<typename T>bool umax(T&a, const T&b){return b<=a?false:(a=b,true);}
template<typename T>bool umin(T&a, const T&b){return b>=a?false:(a=b,true);}

const double PI = acos(-1.0);
const int INF = 1e9 + 7;
const double EPS = 1e-8;

/* -------------------------------------------------------------------------------- */

const int maxn = 1e5 + 7;

struct CartesianTree {
    struct Node {
        int key, value, l, r;
        Node(int key, int value) {
            this->key = key;
            this->value = value;
            l = r = 0;
        }
        Node() {}
    };
    Node tree[maxn];
    int sz;
    stack<int> S;
    void build(int a[], int n) {
        while (!S.empty()) S.pop();
        tree[0] = Node(- 1, - INF);
        S.push(0);
        sz = 0;
        for (int i = 0; i < n; i ++) {
            tree[++ sz] = Node(i, a[i]);
            int last = 0;
            /** 小根堆 区间最小值*/
            while (tree[S.top()].value >= tree[sz].value) {
                last = S.top();
                S.pop();
            }
            tree[sz].l = last;
            tree[S.top()].r = sz;
            S.push(sz);
        }
    }
    Node &operator [] (const int x) {
        return tree[x];
    }
};
CartesianTree ct;

ll ans;

int dfs(int rt) {
    int cnt = 1;
    if (ct[rt].l) cnt += dfs(ct[rt].l);
    if (ct[rt].r) cnt += dfs(ct[rt].r);
    umax(ans, (ll)cnt * ct[rt].value);
    return cnt;
}

int a[maxn];

int main() {
#ifndef ONLINE_JUDGE
    freopen("in.txt", "r", stdin);
    //freopen("out.txt", "w", stdout);
#endif // ONLINE_JUDGE
    int n;
    while (cin >> n, n) {
        for (int i = 0; i < n; i ++) {
            scanf("%d", a + i);
        }
        ct.build(a, n);
        ans = 0;
        dfs(0);
        cout << ans << endl;
    }
    return 0;
}