Alternate Tree Fruiting — Problem Statement & Solution Guide

#include <bits/stdc++.h>
using namespace std;
long long kadane(const vector<int>& v){
    long long best = v[0];
    long long cur = v[0];
    for(size_t i=1;i<v.size();++i){
        cur = max<long long>(v[i], cur+v[i]);
        best = max(best, cur);
    }
    return best;
}
long long maxFruitSum(const vector<int>& treeFruits){
    if(treeFruits.empty()) return 0;
    vector<int> even, odd;
    for(size_t i=0;i<treeFruits.size();++i){
        if(i%2==0) even.push_back(treeFruits[i]);
        else odd.push_back(treeFruits[i]);
    }
    long long ans = LLONG_MIN;
    if(!even.empty()) ans = max(ans, kadane(even));
    if(!odd.empty()) ans = max(ans, kadane(odd));
    return ans;
}
int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n; if(!(cin>>n)) return 0; vector<int> a(n); for(int i=0;i<n;++i)cin>>a[i];
    cout<<maxFruitSum(a);
    return 0;
}

import java.io.*;
import java.util.*;
public class Main {
    private static long kadane(int[] arr){
        long best = arr[0];
        long cur = arr[0];
        for(int i=1;i<arr.length;i++){
            cur = Math.max(arr[i], cur + arr[i]);
            best = Math.max(best, cur);
        }
        return best;
    }
    public static long maxFruitSum(int[] treeFruits){
        if(treeFruits.length==0) return 0;
        int evenCount = (treeFruits.length+1)/2;
        int oddCount = treeFruits.length/2;
        int[] even = new int[evenCount];
        int[] odd = new int[oddCount];
        int ei=0, oi=0;
        for(int i=0;i<treeFruits.length;i++){
            if(i%2==0) even[ei++]=treeFruits[i];
            else odd[oi++]=treeFruits[i];
        }
        long ans = Long.MIN_VALUE;
        if(even.length>0) ans = Math.max(ans, kadane(even));
        if(odd.length>0) ans = Math.max(ans, kadane(odd));
        return ans;
    }
    public static void main(String[] args) throws Exception{
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String line = br.readLine();
        if(line==null||line.isEmpty()) return;
        int n = Integer.parseInt(line.trim());
        int[] arr = new int[n];
        StringTokenizer st = new StringTokenizer(br.readLine());
        for(int i=0;i<n;i++) arr[i]=Integer.parseInt(st.nextToken());
        System.out.print(maxFruitSum(arr));
    }
}

def max_fruit_sum(treeFruits):
    if not treeFruits:
        return 0
    even = treeFruits[0::2]
    odd = treeFruits[1::2]
    def kadane(arr):
        best = cur = arr[0]
        for x in arr[1:]:
            cur = max(x, cur + x)
            best = max(best, cur)
        return best
    ans = max(kadane(even), kadane(odd) if odd else float('-inf'))
    return ans
if __name__ == "__main__":
    import sys
    data = sys.stdin.read().strip().split()
    if not data:
        sys.exit(0)
    it = iter(data)
    n = int(next(it))
    arr = [int(next(it)) for _ in range(n)]
    print(max_fruit_sum(arr))

function maxFruitSum(treeFruits){
    if(treeFruits.length===0) return 0;
    const even=[], odd=[];
    for(let i=0;i<treeFruits.length;i++){
        if(i%2===0) even.push(treeFruits[i]);
        else odd.push(treeFruits[i]);
    }
    const kadane = arr=>{
        let best=arr[0], cur=arr[0];
        for(let i=1;i<arr.length;i++){
            cur = Math.max(arr[i], cur+arr[i]);
            best = Math.max(best, cur);
        }
        return best;
    };
    let ans = -Infinity;
    if(even.length) ans = Math.max(ans, kadane(even));
    if(odd.length) ans = Math.max(ans, kadane(odd));
    return ans;
}
const fs = require('fs');
const input = fs.readFileSync(0,'utf8').trim().split(/\s+/).map(Number);
if(input.length===0) process.exit(0);
let idx=0; const n=input[idx++]; const arr=input.slice(idx, idx+n);
console.log(maxFruitSum(arr));