POJ 3040 贪心

 1 #include <map>
 2 #include <set>
 3 #include <cmath>
 4 #include <queue>
 5 #include <stack>
 6 #include <cstdio>
 7 #include <string>
 8 #include <vector>
 9 #include <cstdlib>
10 #include <cstring>
11 #include <sstream>
12 #include <iostream>
13 #include <algorithm>
14 #include <functional>
15 using namespace std;
16 #define rep(i,a,n) for (int i=a;i<n;i++)
17 #define per(i,a,n) for (int i=n-1;i>=a;i--)
18 #define all(x) (x).begin(),(x).end()
19 #define pb push_back
20 #define mp make_pair
21 #define lson l,m,rt<<1  
22 #define rson m+1,r,rt<<1|1 
23 typedef long long ll;
24 typedef vector<int> VI;
25 typedef pair<int, int> PII;
26 const ll MOD = 1e9 + 7;
27 const int INF = 0x3f3f3f3f;
28 const int MAXN = 5e4 + 7;
29 // head
30 
31 struct Coin {
32     int v, b;
33     const bool operator<(const Coin &c) const {
34         return v < c.v;
35     }
36 }a[30];
37 
38 int use[30];
39 
40 int main() {
41     int n, c;
42     cin >> n >> c;
43     rep(i, 0, n) scanf("%d%d", &a[i].v, &a[i].b);
44     int ans = 0;
45     rep(i, 0, n) if (a[i].v >= c) {
46         ans += a[i].b;
47         a[i].b = 0;
48     }
49     sort(a, a + n);
50     while (1) {
51         int sum = c;
52         memset(use, 0, sizeof(use));
53         per(i, 0, n) if (a[i].b && sum) {
54             use[i] = min(a[i].b, sum / a[i].v);
55             sum -= use[i] * a[i].v;
56         }
57         rep(i, 0, n) if (a[i].b && sum) {
58             int t = min(a[i].b - use[i], (sum + a[i].v - 1) / a[i].v);
59             sum -= t*a[i].v;
60             use[i] += t;
61         }
62         if (sum > 0) break;
63         int x = INF;
64         rep(i, 0, n) if (use[i]) x = min(x, a[i].b / use[i]);
65         ans += x;
66         rep(i, 0, n) if (use[i]) a[i].b -= x*use[i];
67     }
68     cout << ans << endl;
69     return 0;
70 }