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PKU 1190 生日蛋糕

問題:
http://acm.pku.edu.cn/JudgeOnline/problem?id=1190

思路:
DFS+減枝，好題

代碼:

1 /*
2 * N = R[1]^2*H[1] + R[2]^2*H[2] +

+ R[M]^2*H[M]
3 * S = R[1]^2 + 2R[1]*H[1] + 2R[2]*H[2] +

+ 2R[M]H[M]
4  */
5 #include<stdio.h>
6 #include<stdlib.h>
7 #include<string.h>
8 #include<math.h>
9 #define MAX_LEVEL 21
10 #define INF 0x7FFFFFFF
11 /* from top level to the i[th] level, the minimum total volumn and area */
12 int min_volumn[MAX_LEVEL], min_area[MAX_LEVEL];
13 int n, m;
14 int rt;
15
16 void
17 init()
18 {
19     int i;
20     rt = INF;
21     min_volumn[0] = min_area[0] = 0;
22     for(i=1; i<MAX_LEVEL; i++) {
23         min_volumn[i] = min_volumn[i-1] + i*i*i;
24         min_area[i] = min_area[i-1] + 2*i*i;
25     }
26 }
27
28 /* from bottom(m[th] level) to the top */
29 void
30 dfs(int level, int last_r, int last_h, int cur_volumn, int cur_area)
31 {
32     int r, h, tmp, v, a;
33     if(cur_volumn+min_volumn[level]>n || cur_area+min_area[level]>=rt)
34         return;
35     /* ADD this pruning according the volumn&area formula */
36     if(2*(n-cur_volumn)/last_r+cur_area >= rt)
37         return;
38     if(level==0) {
39         if(cur_volumn == n)
40             rt = cur_area<rt ? cur_area : rt;
41         return;
42     }
43     /* the minimal r in [level] would be level */
44     for(r=last_r-1; r>=level; r--) {
45         tmp = (int)((n-cur_volumn-min_volumn[level-1])/(double)(r*r));
46         tmp = tmp>(last_h-1) ? (last_h-1) : tmp;
47         for(h=tmp; h>=level; h--) {
48             v = r*r*h;
49             a = 2*r*h;
50             if(level == m)
51                 a += (r*r);
52             dfs(level-1, r, h, cur_volumn+v, cur_area+a);
53         }
54     }
55 }
56
57 int
58 main(int argc, char **argv)
59 {
60     int max_m_r, max_m_h;
61     while(scanf("%d %d", &n, &m) != EOF) {
62         init();
63         max_m_r = (int)(sqrt((n-min_volumn[m-1])/(double)m)) + 1;
64         max_m_h = (int)((n-min_volumn[m-1])/(double)(m*m)) + 1;
65         dfs(m, max_m_r, max_m_h, 0, 0);
66         if(rt == INF)
67             printf("0\n");
68         else
69             printf("%d\n", rt);
70     }
71 }

posted on 2010-08-03 12:33 simplyzhao 閱讀(515) 評論(0) 編輯收藏引用所屬分類: B_搜索

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