【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][105];

typedef struct {
    char name[105];
    int dead, need;
} homework_st;

homework_st homeworks[MAXNUM];

void printCourse(int end) {
    int top=0, now=end, id, tmp;

    while (now) {
        id = now ^ dps[now].pre;
        tmp = 0;
        while (id) {
            id = id>>1;
            ++tmp;
        }
        strcpy(stack[top++], homeworks[tmp-1].name);
        now = dps[now].pre;
    }

    while (top) {
        --top;
        printf("%s
", 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=0; i<n; ++i)
            scanf("%s %d %d", homeworks[i].name, &homeworks[i].dead, &homeworks[i].need);
        memset(visit, 0, sizeof(visit));
        len = 1<<n;
        dps[0].pre = -1;
        dps[0].reduce = 0;
        dps[0].complete = 0;
        visit[0] = 1;
        // 0~len-1
        for (i=0; i<len-1; ++i) {
            for (j=0; j<n; ++j) {
                code = 1<<j;
                // code is not done
                if ((i&code) == 0) {
                    k = i|code;
                    complete = dps[i].complete + homeworks[j].need;
                    tmp = complete - homeworks[j].dead;
                    if (tmp < 0)
                        tmp = 0;
                    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] = 1;
                        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
", i,dps[i].pre,dps[i].reduce,dps[i].complete);
        */
        printf("%d
", dps[len-1].reduce);
        printCourse(len-1);
    }

    //fclose(fout);
    return 0;
}