hdu 1455 sticks

经典剪枝题目，注释的别人代码。还是得自己多敲。反思，反思！

 1 #include "iostream"

 2 #include "algorithm"

 3 #include "memory.h"

 4 using namespace std;

 5 

 6 int sticks[64],n,len,num;

 7 bool used[64];

 8 

 9 bool cmp(int a,int b)

10 {

11     return a > b;

12 }

13 

14 bool dfs(int cur,int left,int level)

15 {  //cur: 当前已经计算的木棒编号，left:该段还剩的长度，level:已经成功的木棒数

16     if (left == 0) {//匹配一根木棒成功

17         if (level == num-2)  return true;

18         for (cur = 0; used[cur];cur++);//找到下一个未访问过的长度

19         used[cur] = true;

20         if (dfs(cur+1,len-sticks[cur],level+1))

21             return true;

22         used[cur] = false;              //回溯

23         return false;

24     } else {

25             if (cur >= n-1) return false;

26             for (int i = cur;i < n; ++ i) {//剪枝

27                 if (used[i]) continue;      //访问过的长度

28                 if (sticks[i] == sticks[i-1] && !used[i-1]) continue; //相等的长度已经搜过的不搜

29                 if (sticks[i] > left) continue;                     //大于达到len的生育长度

30                 used[i] = true;

31                 if (dfs(i,left-sticks[i],level)) return true;

32                 used[i] = false;        //回溯

33             }

34         return false;

35     }

36 }

37 int main()

38 {

39     while (cin >> n,n) {

40         int sum = 0;

41         for (int i = 0;i < n; ++ i) {

42             cin >> sticks[i];

43             if(sticks[i]>50)

44             {

45                 n--;i--;continue;

46             }

47             sum += sticks[i];

48         }

49         sort(sticks,sticks + n,cmp);//剪枝

50         bool end = false ;

51         for (len = sticks[0]; len <= sum/2; len++) {

52             if (sum%len == 0) {     //剪枝

53                 used[0] = true;

54                 num = sum/len;

55                 if (dfs(0,len-sticks[0],0)) {

56                     end = true;

57                     cout << len << endl;

58                     break;

59                 }

60                 used[0] = false;    //回溯

61             }

62         }

63         if (!end) cout << sum << endl;

64         memset(used,0,sizeof(used));

65     }

66     return 0;

67 }

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