JZOJ 3463. 【NOIP2013模拟联考5】军训

 1 #include <cstdio>
 2 #include <iostream>
 3 #include <string>
 4 #include <cstring>
 5 #define LL long long
 6 #define N 20007
 7 using namespace std;
 8 LL n, limit, h[N], g[N], sum[N], num[N], z[N], ans, mid, f[N];
 9 int next[N];
10 
11 LL get(int t)
12 {
13     LL tl = t, tr = n;
14     while (tl < tr)
15     {
16         LL mi = (tl + tr) / 2;
17         if (sum[mi] - sum[t - 1] >= mid) tr = mi;
18         else tl = mi + 1;
19     }
20     return tl;
21 }
22 
23 bool check()
24 {
25     memset(f, 0x7f7f7f7f, sizeof(f));
26     f[1] = 0;
27     for (int i = 1; i <= n; i++)
28     {
29         int k = get(i);
30         int x = i;
31         int ma = h[i];
32         if (sum[k] - sum[i - 1] > mid)    k--;
33         while (x <= k)
34         {
35             f[x] = min(f[x], f[i] + ma);
36             ma = h[x];
37             x = next[x];
38         }
39         f[k + 1] = min(f[k + 1], f[i] + ma);
40     }
41     if (f[n + 1] <= limit)    return 1;
42     return 0;
43 }
44 
45 int main()
46 {
47     scanf("%lld%lld", &n, &limit);
48     for (int i = 1; i <= n; i++)
49     {
50         scanf("%lld%lld", &h[i], &g[i]);
51         sum[i] = sum[i - 1] + g[i];
52     }
53     int tail = 1;
54     z[1] = 1e9 + 7;
55     num[1] = n + 1;
56     for (int i = n; i >= 1; i--)
57     {
58         while (h[i] >= z[tail])    tail--;
59         next[i] = num[tail];
60         tail++;
61         z[tail] = h[i];
62         num[tail] = i;
63     }
64     ans = sum[n];
65     LL tl = 1, tr = ans;
66     while (tl < tr)
67     {
68         mid = (tl + tr) / 2;
69         if (check())    
70         {
71             if (mid < ans)    ans = mid;
72             tr = mid;
73         }
74         else  tl = mid + 1;    
75     }
76     printf("%lld", tl);
77 }