Submission #1293091

#TimeUsernameProblemLanguageResultExecution timeMemory
1293091hahaBigger segments (IZhO19_segments)C++20
27 / 100
1600 ms109972 KiB
#include <bits/stdc++.h>
#define f first
#define s second
#define ll long long
using namespace std;
const int maxn=3e3+5;

int n;
int a[maxn];
int dp[maxn][maxn],tree[4*maxn][maxn];
ll sum[maxn];

void update(int id,int l,int r,int pos,int type,int val)
{
    if(r<pos||pos<l) return;
    if(l==r){
        tree[id][type]=val;
        return;
    }
    int mid=(l+r)/2;
    update(id*2,l,mid,pos,type,val);
    update(id*2+1,mid+1,r,pos,type,val);
    tree[id][type]=max(tree[id*2][type],tree[id*2+1][type]);
}

int get(int id,int l,int r,int u,int v,int type)
{
    if(r<u||v<l) return -1e9;
    if(u<=l&&r<=v) return tree[id][type];
    int mid=(l+r)/2;
    return max(get(id*2,l,mid,u,v,type),get(id*2+1,mid+1,r,u,v,type));
}

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);cout.tie(0);
    cin>>n;
    for(int i=1;i<=n;i++){
        cin>>a[i];
        sum[i]=sum[i-1]+a[i];
    }
    for(int i=0;i<=n;i++){
        for(int j=0;j<=n;j++){
            dp[i][j]=-1e9;
            update(1,1,n,i,j,-1e9);
        }
    }
    int ans=0;
    for(int i=1;i<=n;i++){
        dp[1][i]=1;
        update(1,1,n,1,i,1);
    }
    for(int i=2;i<=n;i++){
        for(int j=2;j<=i;j++){
            /*
            for(int u=1;u<j;u++){
                if(sum[i]-sum[j-1]>=sum[j-1]-sum[u-1]){
                    // sum[u-1]>=2*sum[j-1]-sum[i]
                    dp[j][i]=max(dp[j][i],dp[u][j-1]+1);
                }
            }
            */
            ll val=2*sum[j-1]-sum[i];
            int pos=lower_bound(sum,sum+j,val)-sum;
            dp[j][i]=max(dp[j][i],get(1,1,n,pos+1,j-1,j-1)+1);
            update(1,1,n,j,i,dp[j][i]);
        }
    }
    for(int i=1;i<=n;i++) ans=max(ans,dp[i][n]);
    cout<<ans;
}
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