【CF1015C】Songs Compression（贪心）

题意：

给定n和m，n组(a[i],b[i])，每一组a[i]可以压缩为b[i]，求最少只需要压缩几个，使得m可以存下所有数据，无解输出-1

思路：按差贪心，排序

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<string>
 4 #include<cmath>
 5 #include<iostream>
 6 #include<algorithm>
 7 #include<map>
 8 #include<set>
 9 #include<queue>
10 #include<vector>
11 using namespace std;
12 typedef long long ll;
13 typedef unsigned int uint;
14 typedef unsigned long long ull;
15 typedef pair<int,int> PII;
16 typedef vector<int> VI;
17 #define fi first
18 #define se second 
19 #define MP make_pair
20 
21 const int N=110000;
22 
23 PII a[N];
24 int n,m;
25 
26 
27 int read()
28 { 
29    int v=0,f=1;
30    char c=getchar();
31    while(c<48||57<c) {if(c=='-') f=-1; c=getchar();}
32    while(48<=c&&c<=57) v=(v<<3)+v+v+c-48,c=getchar();
33    return v*f;
34 }
35 
36 bool cmp(const PII &a,const PII &b)
37 {
38     return a.fi-a.se>b.fi-b.se;
39 }
40 
41 int main()
42 {
43   //freopen("1.in","r",stdin);
44   //freopen("1.out","w",stdout);
45   scanf("%d%d",&n,&m);
46   ll s=0;
47   for(int i=1;i<=n;i++)
48   {
49       int x,y;
50     scanf("%d%d",&x,&y);
51     a[i]=MP(x,y);
52     s+=x;
53   }
54   sort(a+1,a+n+1,cmp);
55   int ans=0;
56   for(int i=1;i<=n;i++)
57   {
58    if(s>m) {s-=a[i].fi-a[i].se; ans++;}
59     else break;
60   }
61   if(s>m) printf("-1");
62    else printf("%d",ans);
63   return 0;
64 }