USACO1.3.1 Mixing Milk (milk)

贪心水题，按单价排序，能买就买

/*ID:shijiey1PROG:milkLANG:C++*/#include <cstdio>#include <cstring>#include <algorithm>using namespace std;struct Node{int all;int unit;bool operator < (const Node &n) const {return unit < n.unit;}};int tot, n;int money = 0;Node arr[5050];int main() {freopen("milk.in", "r", stdin);freopen("milk.out", "w", stdout);scanf("%d %d", &tot, &n);for (int i = 0; i < n; i++) {scanf("%d %d", &arr[i].unit, &arr[i].all);}sort(arr, arr + n);for (int i = 0; i < n; i++) {if (tot - arr[i].all >= 0) {money += arr[i].all * arr[i].unit;tot -= arr[i].all;} else {money += tot * arr[i].unit;break;}}printf("%d\n", money);return 0;}