题解 | #二叉树的后序遍历# 双指针

import java.util.*;

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for(int i=0;i<arr.length;i++){
            arr[i] = sc.nextInt();
        }
        long ans = 0;
        int l=0,r=n-1;
        long lnum=arr[l],rnum=arr[r];
        while(r>=l){
            if(lnum<rnum){
                lnum+=arr[++l];
            }else if(lnum>rnum){
                rnum+=arr[--r];
            }else{
                ans = lnum;
                lnum+=arr[++l];
                rnum+=arr[--r];
            }
        }
        System.out.println(ans);
        
    }
}