【HDOJ】1518 Square

DFS+剪枝。与HDOJ 1455如出一辙。
 1 #include <stdio.h>
 2 #include <stdlib.h>
 3 #include <string.h>
 4 
 5 #define MAXN 25
 6 
 7 int nums[MAXN], n, len, cnt;
 8 char visit[MAXN];
 9 
10 int comp(const void *a, const void *b) {
11     return *(int *)b - *(int *)a;
12 }
13 
14 int dfs(int cnt, int beg, int l) {
15     int i, flg = 0;
16     if (cnt == 3)
17         return 1;
18     if (l == 0) {
19         for (i=0; i<n; ++i) {
20             if ( !visit[i] ) {
21                 visit[i] = 1;
22                 flg = dfs(cnt+1, i+1, len-nums[i]);
23                 visit[i] = 0;
24                 break;
25             }
26         }
27         return flg;
28     }
29 
30     for (i=beg; i<n; ++i) {
31         if ( !visit[i] ) {
32             if (i && !visit[i-1] && nums[i] == nums[i-1])
33                 continue;
34             if (nums[i] <= l) {
35                 visit[i] = 1;
36                 flg = dfs(cnt, i+1, l-nums[i]);
37                 visit[i] = 0;
38                 if (flg) return 1;
39             }
40         }
41     }
42 
43     return 0;
44 }
45 
46 int main() {
47     int case_n, sum;
48     int i, j;
49 
50     scanf("%d", &case_n);
51 
52     while (case_n--) {
53         scanf("%d", &n);
54         sum = 0;
55         for (i=0; i<n; ++i) {
56             scanf("%d", &nums[i]);
57             sum += nums[i];
58         }
59         if ( sum&3 )
60             printf("no
");
61         else {
62             len = sum>>2;
63             qsort(nums, n, sizeof(int), comp);
64             memset(visit, 0, sizeof(visit));
65             j = 1;
66             for (i=0; i<n; ++i)
67                 if (nums[i] > len) {
68                     j = 0;
69                     break;
70                 }
71             if (!j)
72                 printf("no
");
73             else if ( dfs(0, 0, len) )
74                 printf("yes
");
75             else
76                 printf("no
");
77         }
78     }
79 
80     return 0;
81 }