poj3190 Stall Reservations

我一开始想用线段树，但是发现还要记录每头cow所在的棚......

无奈之下选择正解：贪心。

用priority_queue来维护所有牛棚中结束时间最早的那个牛棚，即可得出答案。

注意代码实现的细节。

 1 #include <cstdio>
 2 #include <algorithm>
 3 #include <queue>
 4 using namespace std;
 5 const int N = 50010;
 6 struct Cow {
 7     int a, b, num;
 8     bool operator < (const Cow& x) const {
 9         return this->a < x.a;
10     }
11     bool operator > (const Cow& x) const {
12         return this->a > x.a;
13     }
14 }c[N];
15 priority_queue< Cow, vector<Cow>, greater<Cow> >Q;
16 int ans[N];
17 int main() {
18     int n, top = 0;
19     scanf("%d", &n);
20     for(int i = 1; i <= n; i++) {
21         scanf("%d%d", &c[i].a, &c[i].b);
22         c[i].num = i;
23     }
24     sort(c + 1, c + n + 1);
25     Cow x;
26     x.a = c[1].b;
27     x.b = ++top;
28     ans[c[1].num] = top;
29     Q.push(x);
30     for(int i = 2; i <= n; i++) {
31         //printf("i:%d c[i].b:%d Q.top().a:%d\n", c[i].num, c[i].b, Q.top().a);
32         if(Q.top().a < c[i].a) {
33             x = Q.top();
34             Q.pop();
35             x.a = c[i].b;
36             ans[c[i].num] = x.b;
37             Q.push(x);
38         }
39         else {
40             x.a = c[i].b;
41             x.b = ++top;
42             ans[c[i].num] = top;
43             Q.push(x);
44         }
45     }
46     printf("%d\n", top);
47     for(int i = 1; i <= n; i++) {
48         printf("%d\n", ans[i]);
49     }
50     return 0;
51 }