【HDOJ】1518 Square

DFS+剪枝。与HDOJ 1455如出一辙。

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

 #define MAXN 25

 int nums[MAXN], n, len, cnt;
 char visit[MAXN];

 int comp(const void *a, const void *b) {
     return *(int *)b - *(int *)a;
 }

 int dfs(int cnt, int beg, int l) {
     int i, flg = ;
     if (cnt == )
         return ;
     if (l == ) {
         for (i=; i<n; ++i) {
             if ( !visit[i] ) {
                 visit[i] = ;
                 flg = dfs(cnt+, i+, len-nums[i]);
                 visit[i] = ;
                 break;
             }
         }
         return flg;
     }

     for (i=beg; i<n; ++i) {
         if ( !visit[i] ) {
             if (i && !visit[i-] && nums[i] == nums[i-])
                 continue;
             if (nums[i] <= l) {
                 visit[i] = ;
                 flg = dfs(cnt, i+, l-nums[i]);
                 visit[i] = ;
                 if (flg) return ;
             }
         }
     }

     return ;
 }

 int main() {
     int case_n, sum;
     int i, j;

     scanf("%d", &case_n);

     while (case_n--) {
         scanf("%d", &n);
         sum = ;
         for (i=; i<n; ++i) {
             scanf("%d", &nums[i]);
             sum += nums[i];
         }
         if ( sum& )
             printf("no\n");
         else {
             len = sum>>;
             qsort(nums, n, sizeof(int), comp);
             memset(visit, , sizeof(visit));
             j = ;
             for (i=; i<n; ++i)
                 if (nums[i] > len) {
                     j = ;
                     break;
                 }
             if (!j)
                 printf("no\n");
             else if ( dfs(, , len) )
                 printf("yes\n");
             else
                 printf("no\n");
         }
     }

     return ;
 }