题目1527：首尾相连数组的最大子数组和

import java.util.Scanner;
import java.io.IOException;
import java.io.FileReader;
import java.io.BufferedReader;

class Main
{
private final static boolean DEBUG = false;

public static void main(String[] args) throws IOException
{
Scanner cin;
int n;
int[] a;

if (DEBUG) {
cin = new Scanner(new BufferedReader(new FileReader("d:\\OJ\\uva_in.txt")));
} else {
cin = new Scanner(System.in);
}

while (cin.hasNext()) {
n = cin.nextInt();

a = new int
;
for (int i = 0; i < n; i++) {
a[i] = cin.nextInt();
}

int sum1, min;
sum1 = min = a[0];
int index = 0;
for (int i = 1; i < n; i++) {
if (sum1 < 0) {
sum1 += a[i];
} else {
sum1 = a[i];
}

if (sum1 < min) {
min = sum1;
index = i;
}
}

int[] sum = new int
;
int max = sum[(index + 1) % n] = a[(index + 1) % n];
for (int i = 2; i < n; i++) {
int prev = (index + i - 1) % n;
int cur = (index + i) % n;
if (sum[prev] > 0) {
sum[cur] = sum[prev] + a[cur];
} else {
sum[cur] = a[cur];
}

max = Math.max(max, sum[cur]);
}

int b, sum2;
b = sum2 = a[0];
for (int i = 1; i < n; i++) {
if (sum2 > 0) {
sum2 += a[i];
} else {
sum2 = a[i];
}

if (sum2 > b) {
b = sum2;
}
}

if (b > max) max = b;
if (max < 0) max = 0;

System.out.println(max);
}
}
}