USACO 1.3.1 Mixing Milk (milk)

1、贪心算法

2、优化解：读入数据时将相同价格合并，计算时不需排序。

/*ID: gengjia1LANG: CTASK: milk*/#include <stdio.h>#include <stdlib.h>//#define NDEBUG#include <assert.h>int N, M;struct FARMER{int price;int amount;};int farmercmp(const void *fa, const void *fb){struct FARMER *a, *b;a = (struct FARMER *)fa;b = (struct FARMER *)fb;if(a->price > b->price)return 1;if(a->price < b->price)return -1; return 0;}int main(void) {FILE *fin = fopen ("milk.in", "r");FILE *fout = fopen ("milk.out", "w");struct FARMER *F;int price = 0;int ca = 0;int i;fscanf (fin, "%d", &N);assert(N >= 0);assert(N <= 2000000);fscanf (fin, "%d", &M);assert(M >= 0);assert(M <= 5000);F = (struct FARMER *)malloc(M * sizeof(struct FARMER));for(i = 0; i < M; i++){fscanf(fin, "%d %d", &F[i].price, &F[i].amount);}qsort(F ,M, sizeof(struct FARMER), farmercmp);for(i = 0; i < M && ca < N; i++){ca += F[i].amount;price += F[i].price * F[i].amount;}if(ca > N){price -= (ca - N) * F[--i].price;}fprintf(fout, "%d/n", price);fclose(fin);fclose(fout);exit(0);}