Cattle off-line programming _ the largest continuous sub-arrays and

Topics address

The largest sub-segment and demand

• You can be greedy, dp and partition.
• dp practices and greedy in fact exactly the same ... do not know is not dp.

code1 (greedy)

#include <bits/stdc++.h>
using namespace std;
const int N=1e5+50;
int n,a[N];
int main(){
    scanf("%d",&n);
    for(int i=1;i<=n;i++){
        scanf("%d",&a[i]);
    }
    int ans=-0x3f3f3f3f;
    int p=0;
    for(int i=1;i<=n;i++){
        p+=a[i];
        ans=max(ans,p);
        if(p<0){
            p=0;
        }
    }
    printf("%d\n",ans);
    return 0;
}

code2 (partition)

#include <bits/stdc++.h>
using namespace std;
const int N=1e5+50;
int n,a[N];
int sum(int l,int r){
    if(l==r){
        return a[l];
    }
    int mid=(l+r)/2;
    int lsum=sum(l,mid);
    int rsum=sum(mid+1,r);
    int ls=0;
    int rs=0;
    int tmp=0;
    for(int i=mid;i>=l;i--){
        tmp+=a[i];
        ls=max(ls,tmp);
    }
    tmp=0;
    for(int i=mid+1;i<=r;i++){
        tmp+=a[i];
        rs=max(rs,tmp);
    }
    int msum=ls+rs;
    return max(msum,max(lsum,rsum));
}
int main(){
    scanf("%d",&n);
    for(int i=1;i<=n;i++){
        scanf("%d",&a[i]);
    }
    printf("%d\n",sum(1,n));
    return 0;
}

code3 (dynamic programming)

#include <bits/stdc++.h>
using namespace std;
const int N=1e5+50;
int n,a[N],dp[N];
int main(){
    scanf("%d",&n);
    for(int i=1;i<=n;i++){
        scanf("%d",&a[i]);
    }
    dp[1]=a[1];
    int ans=dp[1];
    for(int i=2;i<=n;i++){
        if(dp[i-1]>0){
            dp[i]=dp[i-1]+a[i];
        }else{
            dp[i]=a[i];
        }
        ans=max(ans,dp[i]);
    }
    printf("%d\n",ans);
    return 0;
}