USACO Section 2.2: Party Lamps

这题有个小技巧， 按一个键两次等于没按，所以如果depsum > 16的话其实不用做深搜到depsum次，而只要16次就可以了。

  1 /*

  2 ID: yingzho1

  3 LANG: C++

  4 TASK: lamps

  5 */

  6 #include <iostream>

  7 #include <fstream>

  8 #include <string>

  9 #include <map>

 10 #include <vector>

 11 #include <set>

 12 #include <algorithm>

 13 #include <stdio.h>

 14 #include <queue>

 15 #include <cstring>

 16 

 17 using namespace std;

 18 

 19 ifstream fin("lamps.in");

 20 ofstream fout("lamps.out");

 21 

 22 int N, depsum;

 23 

 24 bool check(string s, vector<int> &on, vector<int> &off) {

 25     for (int i = 0; i < on.size(); i++) {

 26         if (s[on[i]] != '1') return false;

 27     }

 28     for (int i = 0; i < off.size(); i++) {

 29         if (s[off[i]] != '0') return false;

 30     }

 31     return s.size();

 32 }

 33 

 34 void dfs(set<string> &res, int c1, int c2, int c3, int c4, string s, vector<int> &on, vector<int> &off, int dep) {

 35     if (check(s, on, off)) {

 36         if (dep <= depsum && (depsum-dep)%2 == 0) {

 37             res.insert(s);

 38             //return;

 39         }

 40     }

 41     if (dep == 4 || dep > depsum) return;

 42     string pre = s;

 43     if (c1 < 1) {

 44         dfs(res, c1+1, c2, c3, c4, s, on, off, dep+1);

 45         for (int i = 0; i < s.size(); i++) {

 46             if (s[i] == '0') s[i] = '1';

 47             else s[i] = '0';

 48         }

 49         dfs(res, c1+1, c2, c3, c4, s, on, off, dep+1);

 50     }

 51 

 52     s = pre;

 53 

 54     if (c2 < 1) {

 55         dfs(res, c1, c2+1, c3, c4, s, on, off, dep+1);

 56         for (int i = 0; i < s.size(); i++) {

 57             if (i % 2 == 1) {

 58                 if (s[i] == '1') s[i] = '0';

 59                 else s[i] = '1';

 60             }

 61         }

 62         dfs(res, c1, c2+1, c3, c4, s, on, off, dep+1);

 63     }

 64 

 65     s = pre;

 66     if (c3 < 1) {

 67         dfs(res, c1, c2, c3+1, c4, s, on, off, dep+1);

 68         for (int i = 0; i < s.size(); i++) {

 69             if (i % 2 == 0) {

 70                 if (s[i] == '1') s[i] = '0';

 71                 else s[i] = '1';

 72             }

 73         }

 74         dfs(res, c1, c2, c3+1, c4, s, on, off, dep+1);

 75     }

 76 

 77     s = pre;

 78     if (c4 < 1) {

 79         dfs(res, c1, c2, c3, c4+1, s, on, off, dep+1);

 80         for (int i = 0; i < s.size(); i++) {

 81             if (i % 3 == 0) {

 82                 if (s[i] == '1') s[i] = '0';

 83                 else s[i] = '1';

 84             }

 85         }

 86         dfs(res, c1, c2, c3, c4+1, s, on, off, dep+1);

 87     }

 88 

 89     s = pre;

 90 }

 91 

 92 int main()

 93 {

 94     fin >> N >> depsum;

 95     string s(N, '1');

 96     int n;

 97     vector<int> on, off;

 98     //cout << N << " " << depsum << endl;

 99     while (fin >> n && n != -1) on.push_back(n-1);

100     while (fin >> n && n != -1) off.push_back(n-1);

101     //for (int i = 0; i < on.size(); i++) cout << on[i] << endl;

102     //for (int i = 0; i < off.size(); i++) cout << off[i] << endl;

103     set<string> res;

104     dfs(res, 0, 0, 0, 0, s, on, off, 0);

105     vector<string> ret;

106     for (set<string>::iterator it = res.begin(); it != res.end(); it++) ret.push_back(*it);

107     sort(ret.begin(), ret.end());

108     if (ret.size() == 0) {

109         fout << "IMPOSSIBLE" << endl;

110         return 0;

111     }

112     for (int i = 0; i < ret.size(); i++) {

113         fout << ret[i] << endl;

114     }

115 

116     return 0;

117 }