【HDOJ】1074 Doing Homework

最开始以为是贪心，不过写到一半发现不对，看了一下讨论，知道需要使用状态压缩DP，现在还没有使用深搜实现（据说可以）晚上实现一下，道理应该是类似的。前面做八数码，至今未果，就说需要状态压缩。这个太神奇了，因为题目的数据量为15，所以采用移位压缩。即100代表第三个（注意index）的转台为完成。RE了很多次，才发现异或后求得的不是index。。。而且原来的输入数据本身就是字典序，不需要再strcmp，就一直RE在那个if了。

 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>

 #define MAXNUM  16
 #define MAXDP   1<<15

 typedef struct {
     int pre;
     int reduce;
     int complete;
 } dp_st;

 dp_st dps[MAXDP];
 char  visit[MAXDP];
 char  stack[MAXNUM][];

 typedef struct {
     char name[];
     int dead, need;
 } homework_st;

 homework_st homeworks[MAXNUM];

 void printCourse(int end) {
     int top=, now=end, id, tmp;

     while (now) {
         id = now ^ dps[now].pre;
         tmp = ;
         while (id) {
             id = id>>;
             ++tmp;
         }
         strcpy(stack[top++], homeworks[tmp-].name);
         now = dps[now].pre;
     }

     while (top) {
         --top;
         printf("%s\n", stack[top]);
     }
 }

 int main() {
     int case_n, n, len;
     int i, j, k, code, tmp, complete, reduce;
     //FILE *fout = fopen("data", "w");

     scanf("%d", &case_n);

     while (case_n--) {
         scanf("%d%*c", &n);
         for (i=; i<n; ++i)
             scanf("%s %d %d", homeworks[i].name, &homeworks[i].dead, &homeworks[i].need);
         memset(visit, , sizeof(visit));
         len = <<n;
         dps[].pre = -;
         dps[].reduce = ;
         dps[].complete = ;
         visit[] = ;
         // 0~len-1
         for (i=; i<len-; ++i) {
             for (j=; j<n; ++j) {
                 code = <<j;
                 // code is not done
                 if ((i&code) == ) {
                     k = i|code;
                     complete = dps[i].complete + homeworks[j].need;
                     tmp = complete - homeworks[j].dead;
                     if (tmp < )
                         tmp = ;
                     reduce = dps[i].reduce + tmp;
                     if ( visit[k] ) {
                         if (reduce < dps[k].reduce) {
                             dps[k].reduce = reduce;
                             dps[k].complete = complete;
                             dps[k].pre = i;
                         }
                         /* No need and tmp need to while(){>>1} again
                         else if (reduce == dps[k].reduce){
                             tmp = dps[k].pre ^ k;
                             if (strcmp(homeworks[j].name, homeworks[tmp].name) < 0) {
                                 dps[k].reduce = reduce;
                                 dps[k].complete = complete;
                                 dps[k].pre = i;
                             }
                         }*/
                     } else {
                         visit[k] = ;
                         dps[k].reduce = reduce;
                         dps[k].complete = complete;
                         dps[k].pre = i;
                     }
                 }
             }
         }
         /*
         for (i=0; i<len; ++i)
             fprintf(fout, "%d: pre=%d,reduce=%d,complete=%d\n", i,dps[i].pre,dps[i].reduce,dps[i].complete);
         */
         printf("%d\n", dps[len-].reduce);
         printCourse(len-);
     }

     //fclose(fout);
     return ;
 }