USACO 1.3.2 Barn Repair (barn1)

1、貪心演算法：先用一塊木板蓋住牛棚，然後，每次從蓋住的範圍內選一個最大的空隙，以空隙為界將木板分成兩塊，重複直到分成m塊或沒有空隙。

/*<br />ID: gengjia1<br />LANG: C<br />TASK: barn1<br />*/<br />#include <stdio.h><br />#include <stdlib.h><br />#include <string.h><br />//#define NDEBUG<br />#include <assert.h><br />#define MAX_STALL 200<br />int M, S, C;<br />/* 降序 */<br />int intcompare (const void * a, const void * b)<br />{<br /> return ( *(int*)b - *(int*)a );<br />}<br />int main(void) {<br />FILE *fin = fopen ("barn1.in", "r");<br />FILE *fout = fopen ("barn1.out", "w");<br />assert(fin != NULL && fout != NULL);<br />int s[MAX_STALL+1] = {0};<br />int d[MAX_STALL] = {0};<br />int current;<br />int last;<br />int minlen;<br />int count = 1; /* 木板的數目 */<br />int i, j;<br />fscanf (fin, "%d", &M);<br />assert(M >= 1);<br />assert(M <= 50);<br />fscanf (fin, "%d", &S);<br />assert(S >= 1);<br />assert(S <= MAX_STALL);<br />fscanf (fin, "%d", &C);<br />assert(C >= 1);<br />assert(C <= S);<br />for(i = 0; i < C; i++)<br />{<br />fscanf(fin, "%d", &current);<br />assert(current <= S);<br />s[i] = current;<br />}<br />/* 對牛棚序號降序排序（升降無所謂，下面必須用到降序，所以這裡一樣） */<br />qsort(s, C, sizeof(int), intcompare);<br />/* 計算相鄰兩個有牛的牛棚的距離 */<br />j = 0;<br />for(i = 0; i < C; i++)<br />{<br />current = s[i];<br />if(i == 0)<br />{<br />minlen = current;<br />last = current;<br />continue;<br />}<br />if(last - current - 1 > 0)<br />{<br />d[j++] = last - current - 1;<br />}<br />last = current;<br />}<br />minlen = minlen - current + 1; /* 一塊木板蓋住所有牛棚的長度 */<br />qsort(d, j, sizeof(int), intcompare);<br />for(i = 0; i < j; i++)<br />{<br />if(count == M)<br />{<br />break;<br />}<br />minlen -= d[i];<br />count += 1;<br />}<br />fprintf(fout, "%d/n", minlen);<br />fclose(fin);<br />fclose(fout);<br />exit(0);<br />}<br />