poj2796（单调栈+树状数组）

#include <stack>
#include <stdio.h>
#include <string.h>
#include <iostream>
#include <algorithm>

using namespace std;
#define ll long long
#define ull unsigned long long
#define cls(x) memset(x,0,sizeof(x))
#define clslow(x) memset(x,-1,sizeof(x))

const int maxn=1e5+100;

int n;

stack<int>st;
ll bit[maxn];
int a[maxn],L[maxn],R[maxn];

int lowbit(int x)
{
    return x&-x;
}

void update(int x,int add)
{
    while(x<=n)
    {
        bit[x]+=add;
        x+=lowbit(x);
    }
}

ll sum(int x)
{
    ll res=0;
    while(x>0)
    {
        res+=bit[x];
        x-=lowbit(x);
    }
    return res;
}

//树状数组求区间和
ll query(int x,int y)
{
    return sum(y)-sum(x-1);
}

//单调栈找出每个值对应的子区间的边界
void solve()
{
    while(!st.empty())  st.pop();
    for(int i=1;i<=n;i++){
        while(st.size()&&a[st.top()]>=a[i]) st.pop();

        if(st.empty())  L[i]=0;
        else            L[i]=st.top();

        st.push(i);
    }
    while(!st.empty())  st.pop();
    for(int i=n;i>=1;i--){
        while(st.size()&&a[st.top()]>=a[i]) st.pop();

        if(st.empty())  R[i]=n+1;
        else            R[i]=st.top();

        st.push(i);
    }
}

void print()
{
    int l,r;
    ll ans=-1;
    for(int i=1;i<=n;i++){
        ll val=query(L[i]+1,R[i]-1)*a[i];
        if(ans<val){
            ans=val;
            l=L[i]+1;
            r=R[i]-1;
        }
    }
    printf("%lld\n",ans);
    printf("%d %d\n",l,r);
}

int main()
{
//    freopen("in.txt","r",stdin);
    while(scanf("%d",&n)!=EOF)
    {
        cls(bit);
        for(int i=1;i<=n;i++){
            scanf("%d",&a[i]);
            update(i,a[i]);
        }

        solve();
        print();
    }
    return 0;
}