USACO Section 1.5: Checker Challenge

这题的关键是对半剪枝

 1 /*

 2 ID: leetcod3

 3 PROG: checker

 4 LANG: C++

 5 */

 6 #include <iostream>

 7 #include <fstream>

 8 #include <string>

 9 #include <map>

10 #include <vector>

11 #include <set>

12 #include <algorithm>

13 #include <queue>

14 #include <cmath>

15 #include <list>

16 #include <cstring>

17 #include <cstdlib>

18 #include <limits>

19 #include <stack>

20 

21 using namespace std;

22 

23 ofstream fout ("checker.out");

24 ifstream fin ("checker.in");

25 

26 int N;

27 bool col[14];

28 int rec[14];

29 int total = 0;

30 int print_total = 0;

31 

32 bool intersect(int dep, int x) {

33     for (int i = 0; i < dep; ++i) {

34         if (dep - i == abs(rec[i]-x)) return true;

35     }

36     return false;

37 }

38 

39 void dfs(int dep, int n) {

40     if (dep == N) {

41         total++;

42         if (print_total++ < 3) {

43             for (int i = 0; i < N-1; ++i) fout << rec[i]+1 << " ";

44             fout << rec[N-1]+1 << endl;

45         }

46         if (N > 6 && rec[0] < N/2) total++;

47         return;

48     }

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

50         if (!col[i] && !intersect(dep, i)) {

51             col[i] = true;

52             rec[dep] = i;

53             dfs(dep+1, N);

54             col[i] = false;

55         }

56     }

57 }

58 

59 int main()

60 {

61     fin >> N;

62     memset(col, false, sizeof(col));

63     memset(rec, 0, sizeof(rec));

64     dfs(0, N > 6? (N+1)/2 : N);

65     fout << total << endl;

66     return 0;

67 }