DFS(剪枝) POJ 1011 Sticks

题目传送门

 /*
     题意：若干小木棍，是由多条相同长度的长木棍分割而成，问最小的原来长木棍的长度；
     DFS剪枝：剪枝搜索的好题！TLE好几次，终于剪枝完全！
         剪枝主要在4和5：4 相同长度的木棍不再搜索；5 若新的搜索连第一条都没组合出来，直接break；
     详细解释：http://blog.csdn.net/lyy289065406/article/details/6647960
                 http://www.cnblogs.com/devil-91/archive/2012/08/03/2621787.html
     这题虐我千百遍，我待她如。。        656K    0MS

     博客随笔第100篇，纪念一下:)
 */
 #include <cstdio>
 #include <iostream>
 #include <cstring>
 #include <map>
 #include <set>
 #include <cmath>
 #include <algorithm>
 using namespace std;

 const int MAXN = ;
 const int INF = 0x3f3f3f3f;
 int a[MAXN];
 bool vis[MAXN];
 int sum;
 int n, cnt;

 bool cmp(int x, int y)
 {
     return x > y;
 }

 bool DFS(int len, int ans, int num, int s)
 {
     if (num == cnt)    return true;

     int pre = -;
     for (int i=s; i<=n; ++i)
     {
         if (vis[i] || a[i] == pre)    continue;        //Cut 4

         vis[i] = true;
         if (ans + a[i] < len)
         {
             if (DFS (len, ans + a[i], num, i) == true)  return true;
             else    pre = a[i];
         }
         else if (ans + a[i] == len)
         {
             if (DFS (len,  , num+, ) == true)  return true;
             else    pre = a[i];
         }
         vis[i] = false;

         if (ans == )    break;        //Cut 5
     }

     return false;
 }

 int main(void)        //POJ 1011 Sticks
 {
     //freopen ("POJ_1011.in", "r", stdin);

     while (scanf ("%d", &n) ==  && n)
     {
         sum = ;    memset (vis, , sizeof (vis));
         for (int i=; i<=n; ++i)
         {
             scanf ("%d", &a[i]);    sum += a[i];
         }
         sort (a+, a++n, cmp);                //Cut 1

         bool flag = false;
         for (int i=a[]; i<=sum-i; ++i)        //Cut 2
         {
             if (sum % i == )                //Cut 3
             {
                 cnt = sum / i;
                 if (DFS (i, , , ) == true)
                 {
                     flag = true;
                     printf ("%d\n", i);    break;
                 }
             }
         }
         if (!flag)    printf ("%d\n", sum);
     }

     return ;
 }

 /*
 6
 5
 */