算法问题实战策略 SORTGAME

地址 https://algospot.com/judge/problem/read/SORTGAME

解答

常规BFS是会超时的  按照书上的提示 应该是打表(居然还有提倡打表的题目)

tle 代码

 #include <iostream>
 #include <vector>
 #include <algorithm>
 #include <queue>
 #include <map>

 using namespace std;

 int n, m;

 int bfs(const vector<int>& v)
 {
     vector<int> sorted = v;
     sort(sorted.begin(), sorted.end());
     queue<vector<int>> q;
     map<vector<int>, int> distance;
     distance[v] = ;
     q.push(v);
     while (!q.empty()) {
         vector<int> here = q.front();
         q.pop();

         if (here == sorted) return distance[here];
         int cost = distance[here];
         //翻转可能的子区间
         for (int i = ; i < v.size(); i++) {
             for (int j = i + ; j <= v.size(); ++j) {
                 reverse(here.begin() + i, here.begin() + j);
                 if (distance.count(here) == ) {
                     distance[here] = cost + ;
                     q.push(here);
                 }
                 reverse(here.begin() + i, here.begin() + j);
             }
         }
     }

     return -;
 }

 int main()
 {
     cin >> n;

     while (n--) {
         cin >> m;
         vector<int> v;
         for (int i = ; i < m; i++) {
             int t;
             cin >> t;
             v.push_back(t);
         }

         cout << bfs(v) << endl;
     }

     return ;
 }

ac代码

 #include <iostream>
 #include <algorithm>
 #include <map>
 #include <queue>
 #include <vector>

 using namespace std;

 map<vector<int>, int> toSort;

 void precalc(int n) {
     vector<int> perm(n);
     for (int i = ; i < n; ++i) perm[i] = i;
     queue<vector<int>> q;
     q.push(perm);
     toSort[perm] = ;
     while (!q.empty()) {
         vector<int> here = q.front();
         q.pop();
         int cost = toSort[here];
         for (int i = ; i < n; i++) {
             for (int j = i + ; j <= n; ++j) {
                 reverse(here.begin() + i, here.begin() + j);
                 if (toSort.count(here) == ) {
                     toSort[here] = cost + ;
                     q.push(here);
                 }
                 reverse(here.begin() + i, here.begin() + j);
             }
         }
     }
 }

 int solve(const vector<int>& perm)
 {
     int n = perm.size();
     vector<int> fixed(n);
     for (int i = ; i < n; ++i) {
         int smaller = ;
         for (int j = ; j < n; ++j)
             if (perm[j] < perm[i])
                 ++smaller;
             fixed[i] = smaller;
     }
     return toSort[fixed];
 }

 int n, m;
 int main()
 {
     cin >> n;
     while (n--) {
         cin >> m;
         precalc(m);
         vector<int> perm;
         for (int i = ; i < m; i++) {
             int t;
             cin >> t;
             perm.push_back(t);
         }
         cout << solve(perm) << endl;
     }

     return ;
 }