USACO 1.3.1 Mixing Milk (milk)

1、貪心演算法

2、最佳化解：讀入資料時將相同價格合并，計算時不需排序。

/*<br />ID: gengjia1<br />LANG: C<br />TASK: milk<br />*/<br />#include <stdio.h><br />#include <stdlib.h><br />//#define NDEBUG<br />#include <assert.h><br />int N, M;<br />struct FARMER{<br />int price;<br />int amount;<br />};<br />int farmercmp(const void *fa, const void *fb)<br />{<br />struct FARMER *a, *b;<br />a = (struct FARMER *)fa;<br />b = (struct FARMER *)fb;</p><p>if(a->price > b->price)<br />return 1;<br />if(a->price < b->price)<br />return -1;<br /> return 0;<br />}<br />int main(void) {<br />FILE *fin = fopen ("milk.in", "r");<br />FILE *fout = fopen ("milk.out", "w");<br />struct FARMER *F;<br />int price = 0;<br />int ca = 0;<br />int i;<br />fscanf (fin, "%d", &N);<br />assert(N >= 0);<br />assert(N <= 2000000);<br />fscanf (fin, "%d", &M);<br />assert(M >= 0);<br />assert(M <= 5000);<br />F = (struct FARMER *)malloc(M * sizeof(struct FARMER));<br />for(i = 0; i < M; i++)<br />{<br />fscanf(fin, "%d %d", &F[i].price, &F[i].amount);<br />}<br />qsort(F ,M, sizeof(struct FARMER), farmercmp);<br />for(i = 0; i < M && ca < N; i++)<br />{<br />ca += F[i].amount;<br />price += F[i].price * F[i].amount;<br />}<br />if(ca > N)<br />{<br />price -= (ca - N) * F[--i].price;<br />}<br />fprintf(fout, "%d/n", price);<br />fclose(fin);<br />fclose(fout);<br />exit(0);<br />}<br />