我重写行不？
签到题，类似于BFS用两个队列维护每种单词前/后是否有逗号向前/后扩展，需要注意如果有句号挡着是不能扩展过去的，不过样例有。
1 #include <bits/stdc++.h> 2 using namespace std; 3 const int maxn = 1e6 + 10; 4 map<string, vector<int>> M; 5 bool pre[maxn], suc[maxn]; 6 bool st[maxn], ed[maxn]; 7 queue<string> QP, QS; 8 set<string> SP, SS; 9 string str[maxn]; 10 11 int main() { 12 string s; 13 getline(cin, s); 14 int l = s.length(), p = 1; 15 st[p] = true; 16 for(int i = 0; i < l; ++i) { 17 if(s[i] == ',') { 18 suc[p] = pre[p + 1] = true; 19 ++p, ++i; 20 } 21 else if(s[i] == '.') { 22 ed[p] = st[p + 1] = true; 23 ++p, ++i; 24 } 25 else if(s[i] == ' ') ++p; 26 else str[p].push_back(s[i]); 27 } 28 for(int i = 1; i < p; ++i) M[str[i]].push_back(i); 29 for(int i = 1; i < p; ++i) { 30 if(pre[i] && SP.find(str[i]) == SP.end()) SP.insert(str[i]), QP.push(str[i]); 31 if(suc[i] && SS.find(str[i]) == SS.end()) SS.insert(str[i]), QS.push(str[i]); 32 } 33 while(!QP.empty() || !QS.empty()) { 34 while(!QP.empty()) { 35 string cur = QP.front(); QP.pop(); 36 vector<int>& pos = M[cur]; 37 for(int i = 0; i < pos.size(); ++i) { 38 int x = pos[i]; 39 if(!st[x]) pre[x] = true; 40 if(x - 1 > 0 && !ed[x - 1] && SS.find(str[x - 1]) == SS.end()) suc[x - 1] = true, SS.insert(str[x - 1]), QS.push(str[x - 1]); 41 } 42 } 43 while(!QS.empty()) { 44 string cur = QS.front(); QS.pop(); 45 vector<int>& pos = M[cur]; 46 for(int i = 0; i < pos.size(); ++i) { 47 int x = pos[i]; 48 if(!ed[x]) suc[x] = true; 49 if(x + 1 < p && !st[x + 1] && SP.find(str[x + 1]) == SP.end()) pre[x + 1] = true, SP.insert(str[x + 1]), QP.push(str[x + 1]); 50 } 51 } 52 } 53 for(int i = 1; i < p; ++i) { 54 cout << str[i]; 55 if(ed[i]) cout << '.'; 56 else if(suc[i]) cout << ','; 57 if(i < p - 1) cout << ' '; 58 else cout << endl; 59 } 60 return 0; 61 }