sicily 1768

//如果队列inSeq中存在i<j<k，使得inSeq[k]<inSeq[i]<inSeq[j]，那么inSeq[i]和inSeq[j]不能被放进同一个栈中 #include <iostream> #include <stack> #include <cmath> #include <cstring> #include <string> using namespace std; #define INF 10000 int color[1010]; bool adj[1010][1010]; int _min[1010]; int n; int inSeq[1010]; stack<int> s1; stack<int> s2; string path; bool dfs(int cur) { for(int i = 0; i < n; i++) { if(adj[cur][i]) { if(color[i] == 0) { color[i] = 3 - color[cur]; if(!dfs(i)) return false; }else if(color[i] == color[cur]) return false; } } return true; } int main() { //freopen("1.txt", "r", stdin); while(cin >> n) { for(int i = 0; i < n; i++) cin >> inSeq[i]; _min[n] = INF; memset(adj, false, sizeof(adj)); memset(color, 0, sizeof(color)); for(int i = n - 1; i >= 0; i--) _min[i] = min(inSeq[i], _min[i + 1]); //找到所有无向边 for(int i = 0; i < n; i++) { for(int j = i + 1; j < n; j++) { if(inSeq[i] < inSeq[j] && inSeq[i] > _min[j + 1]) { adj[i][j] = adj[j][i] = true; } } } //染色 bool ok = true; for(int i = 0; i < n; i++) { if(color[i] == 0) { color[i] = 1; if(!dfs(i)) { ok = false; break; } } } if(!ok) { cout << 0 << endl; continue; } //模拟求解 int out = 0; //输出队列的元素个数 path = ""; for(int i = 0; i < n; i++) { if(color[i] == 1) { path += "a "; s1.push(inSeq[i]); } else { path += "c "; s2.push(inSeq[i]); } while((!s1.empty() && s1.top() == out + 1) || (!s2.empty() && s2.top() == out + 1)) { if(s1.top() == out + 1) { path += "b "; s1.pop(); }else { path += "d "; s2.pop(); } out++; } } path.erase(path.size() - 1, 1); cout << path << endl; } return 0; }