hdu 5280 贪心 O(n)算法

 1 #include <set>
 2 #include <map>
 3 #include <queue>
 4 #include <deque>
 5 #include <cmath>
 6 #include <vector>
 7 #include <string>
 8 #include <cstdio>
 9 #include <cstdlib>
10 #include <cstring>
11 #include <cassert>
12 #include <iostream>
13 #include <algorithm>
14 
15 #define dprint(expr) fprintf(stderr, #expr " = %d\n", expr)
16 
17 using namespace std;
18 
19 typedef long long LL;
20 typedef pair <int, int> PII;
21 
22 const int N = 1e5 + 7;
23 const int INF = 0x3f3f3f3f;
24 const int MOD = 1e9 + 7;
25 const double EPS = 1e-6;
26 const double PI = acos(-1.0);
27 
28 int a[N];
29 LL l[N], r[N];
30 
31 int main(void){
32     int T;
33     scanf("%d", &T);
34     while (T--) {
35         int n, p;
36         scanf("%d%d", &n, &p);
37         for (int i = 1; i <= n; ++i)
38             scanf("%d", &a[i]);
39         l[0] = r[0] = l[n + 1] = r[n + 1] = 0;
40         for (int i = 1; i <= n; ++i)
41             l[i] = max(l[i - 1] + a[i], (LL)a[i]);
42         for (int i = n; i; --i)
43             r[i] = max(r[i + 1] + a[i], (LL)a[i]);
44         LL ans = -INF;
45         for (int i = 1; i <= n; ++i) {
46             ans = max(ans, max(l[i - 1], 0LL) + max(r[i + 1], 0LL) + p);
47         }
48         for (int i = 1; i < n; ++i) {
49             ans = max(ans, l[i]);
50         }
51         for (int i = n; i > 1; --i) {
52             ans = max(ans, r[i]);
53         }
54         printf("%I64d\n", ans);
55     }
56     return 0;
57 }