JAVA题解：

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        }
        
        System.out.println(maxSubarrayWithOneFlip(a));
        sc.close();
    }
    
    public static int maxSubarrayWithOneFlip(int[] a) {
        if (a.length == 0) return 0;
        
        int dp0 = a[0];     // 未取反
        int dp1 = -a[0];    // 正在取反
        int dp2 = a[0];     // 已取反
        int ans = Math.max(Math.max(dp0, dp1), dp2);
        
        for (int i = 1; i < a.length; i++) {
            int prev0 = dp0, prev1 = dp1, prev2 = dp2;
            
            dp0 = Math.max(prev0 + a[i], a[i]);
            dp1 = Math.max(prev1 - a[i], prev0 - a[i]);
            dp2 = Math.max(prev2 + a[i], prev1 + a[i]);
            
            ans = Math.max(ans, Math.max(Math.max(dp0, dp1), dp2));
        }
        
        return ans;
    }
}