[Codeforces] 1015C. Songs Compression

題目URL: http://codeforces.com/contest/1015/problem/C
相減sort後，aa總和從小減到大一邊記數，比b小就輸出

#include<bits/stdc++.h>
using namespace std;
#define int  long long
int aa,bb,str[100005];
signed main()
{
    int a,b,total=0,totala=0,tot=0;
    cin >> a >> b;
    for(int i=0;i<a;i++)
    {
        cin >> aa >> bb;

        str[i]=aa-bb;

        total+=bb;

        totala+=aa;

    }
    sort(str,str+a);
    if(total>b)
        cout << -1 << endl;

    else
    {

        for(int i=a-1;i>=0;i--)

        {

            //cout << str[i] << endl;

            if(totala<=b)

                break;

            totala-=str[i];

            tot++;

        }

        cout << tot << endl;

    }
    return 0;
}