POJ 2479 不相交最大子段和

//#pragma comment(linker, "/STACK:16777216") //for c++ Compiler
#include <stdio.h>
#include <iostream>
#include <cstring>
#include <cmath>
#include <stack>
#include <queue>
#include <vector>
#include <algorithm>
#define ll long long
#define Max(a,b) (((a) > (b)) ? (a) : (b))
#define Min(a,b) (((a) < (b)) ? (a) : (b))
#define Abs(x) (((x) > 0) ? (x) : (-(x)))

const int INF  = 0x3f3f3f3f;
int a[50001], left[50001], right[50001];
int main(){
    int i, j, t, k, n, m;
    scanf("%d",&t);
    while(t--){
        scanf("%d",&n);
        for(i = 0; i < n; ++i)  scanf("%d",&a[i]);
        left[0] = a[0];
        for(i = 1; i < n; ++i){
            if(left[i - 1] < 0)
                left[i] = a[i];
            else
                left[i] = left[i - 1] + a[i];
        }
        for(i = 1; i < n; ++i){
            left[i] = Max(left[i - 1], left[i]);    //Max segment sum
        }
        right[n - 1] = a[n - 1];
        for(i = n - 2; i >= 0; --i){
            if(right[i + 1] < 0)
                right[i] = a[i];
            else
                right[i] = right[i + 1] + a[i];
        }
        for(i = n - 2; i > 0; --i){
            right[i] = Max(right[i + 1], right[i]); //Max segment sum
        }
        int MAX = -INF;
        for(i = 1; i < n; ++i){
            MAX = Max(MAX, left[i - 1] + right[i]);
        }
        printf("%d\n",MAX);
    }
    return 0;
}