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\n");
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\n");
73 else if ( dfs(0, 0, len) )
74 printf("yes\n");
75 else
76 printf("no\n");
77 }
78 }
79
80 return 0;
81 }
时间： 2024-09-30 15:39:22