获得最多的奖金

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.lang.reflect.Array;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Scanner;

/**
  好多人用的双指针，感觉这题前缀和直接出答案 
*/
public class Main {

    static int n, N = 200010;
    static long max;
    static long[] s = new long[N];
    static HashMap<Long, Integer> map = new HashMap<>();
    public static void main(String[] args) throws IOException {
        BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
        n = Integer.parseInt(bf.readLine());
        String[] arr = bf.readLine().split(" ");
        for(int i = 1; i <= n; i ++){
            s[i] += s[i - 1] + Integer.parseInt(arr[i - 1]);
            map.put(s[i], i);
        }

        for(int i = n; i >= 1; i --){
            long cur = s[n] - s[i - 1];
            if(map.containsKey(cur) && map.get(cur) < i && cur > max)
                  max = cur;
        }
        System.out.println(max);
    }

}

Java;双指针;前缀和算法

import java.util.*;
public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long[] d = new long[n];
        long[] sum = new long[n];
        //计算前缀和，包含本身
        for(int i=0;i<n;i++){
            d[i] = sc.nextInt();
            if(i == 0)
                sum[i] = d[i];
            else
                sum[i] = sum[i-1] + d[i];
        }
        //双指针，计算最大奖金和
        long max = 0;
        int start = 0,end = n-1;
        while(start < end){
            if(sum[start] < (sum[n-1] - sum[end-1])){
                start++;
            }
            else if(sum[start] == (sum[n-1] - sum[end-1])){
                max = Math.max(max,sum[start]);
                start++;
                end--;
            }
            else
                end--;
        }
        System.out.println(max);
    }
}

import java.util.*;

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        while(sc.hasNext()){
            //数据的个数
            int n = Integer.valueOf(sc.nextLine());
            String[] str = sc.nextLine().split(" ");
            //数据数组
            int[] nums = new int[n];
            long max = 0;
            for(int i =0;i<n;i++){
                nums[i]=Integer.valueOf(str[i]);
            }
            max = select(nums,0,nums.length-1);
            System.out.println(max);
        }
    }
    //双指针
    public static long select(int[] nums,int low,int high){
        long max = 0;
        int left = 0;
        int right = 0;
        while(low<=high){
            if((nums[low]+left)<(nums[high]+right)){
                left +=nums[low];
                low++;
            }else if((nums[low]+left)>(nums[high]+right)){
                right+=nums[high];
                high--;
            }else{
                left += nums[low];
                max += left;
                low++;
                high--;
                left = 0;
                right = 0;
            }
        }
        return max;
    }
}

import java.util.*;
public class Main{
    //思路：
    //1.定义左指针跟右指针，分别指向第一个红包和最后一个红包
    //2.左指针指向数据和 > 右指针指向数据和，左指针++；
    //3.左指针指向数据和 < 右指针指向数据和，右指针--；
    //4.左指针指向数据和 = 右指针指向数据和，左指针++，右指针--；
    //约束条件是左指针 < 右指针。
    //需要注意的是所有求和的值都要设为long型，会超过int最大范围。
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();//红包个数
        int[] d = new int[n];//每个红包奖金数额
        for(int i = 0; i < n; i++){
            d[i] = sc.nextInt();
        }
        int left = 0;
        long leftSum = d[left];
        int right = n - 1;
        long rightSum = d[right];
        long max = 0;
        while(left < right){
            if(leftSum < rightSum){
                left++;
                leftSum += d[left];
            }
            if(leftSum > rightSum){
                right--;
                rightSum += d[right];
            }
            if(leftSum == rightSum){
                max = leftSum;
                left++;
                right--;
                leftSum += d[left];
                rightSum += d[right];
            }
        }
        System.out.println(max);
    }
}

import java.util.*;
public class Main{
    public static void main(String[] args){
        Scanner input = new Scanner(System.in);
        int n = input.nextInt();
        long[] a = new long[n];
        for (int i = 0; i < n; i++) {
            a[i] = input.nextLong();
        }
        long ret = 0L;

        int left = 0;
        int right = n-1;
        int res = 0;
        
        long al = a[left];
        long ar = a[right];
        
        while(left<right){
            if(al<ar){
                left++;
                al+=a[left];
            }else if(al>ar){
                right--;
                ar+=a[right];
                
            }else if(al==ar){
                res = left;
                ret = al;
                left++;
                al+=a[left];
                right--;
                ar+=a[right];
                
            }
        }
        long ret1 = 0L;
        for(int i = 0;i<=res;i++){
            ret1 += a[i];
        }
        if(ret == ret1){
            System.out.println(ret1);
        }else{
            System.out.println("no");
        }
        
    }
}

/*
使用low和high分别从前到尾扫描，若前面的和和后面部分的和相等就标记它们的值，遇到大的就更新max
直到low和high相等。
*/  import java.util.Scanner;
public class Main{
        public static void main(String[] args){
                Scanner sc = new Scanner(System.in);
                int n = sc.nextInt();
                long[] arr = new long[n];
                for(int i=0;i<n;i++)
                        arr[i]=sc.nextLong();
                int low=0,high=n-1;
                long max=0,lowSum=arr[low],highSum=arr[high];
                while(low<=high){
                        if(lowSum>highSum)
                                highSum+=arr[--high];
                        else if(lowSum<highSum)
                                lowSum+=arr[++low];
                        else{
                                max=lowSum;
                                lowSum+=arr[++low];
                                highSum+=arr[--high];
                        }
                }
                System.out.println(max);
        }
}