CF615C Running Track

思路：

kmp + 二分。

实现：

 #include <iostream>
 #include <cstdio>
 #include <algorithm>
 #include <vector>
 using namespace std;
 const int MAXN = ;
 int neXt[MAXN];

 void getNext(string s)
 {
     int n = s.length();
     neXt[] = -;
     int k = -, j = ;
     while (j < n)
     {
         if (k == - || s[j] == s[k])
         {
             j++; k++;
             if (s[j] != s[k]) neXt[j] = k;
             else neXt[j] = neXt[k];
         }
         else
         {
             k = neXt[k];
         }
     }
 }

 int kmp(string s, string p)
 {
     int i = , j = ;
     int m = s.length(), n = p.length();
     while (i < m && j < n)
     {
         if (j == - || s[i] == p[j]) i++, j++;
         else j = neXt[j];
     }
     if (j == n) return i - j;
     return -;
 }

 bool solve(string x, string y, vector<pair<int, int>> & ans)
 {
     string z(x);
     reverse(z.begin(), z.end());
     int m = x.length();
     int n = y.length();
     int start = ;
     while (start < n)
     {
         int l = , r = n - start, res = , pos = -;
         bool flg = true;
         while (l <= r)
         {
             int mid = (l + r) >> ;
             string tmp = y.substr(start, mid);
             getNext(tmp);
             int p = kmp(x, tmp);
             if (p != -)
             {
                 res = mid; pos = p; flg = true; l = mid + ;
             }
             else if ((p = kmp(z, tmp)) != -)
             {
                 res = mid; pos = p; flg = false; l = mid + ;
             }
             else r = mid - ;
         }
         if (!res) return false;
         if (flg) ans.push_back(pair<int, int>(pos + , pos + res));
         else ans.push_back(pair<int, int>(m - pos, m - pos - res + ));
         start += res;
     }
     return true;
 }

 int main()
 {
     string x, y;
     cin >> x >> y;
     vector<pair<int, int>> res;
     if (solve(x, y, res))
     {
         cout << res.size() << endl;
         for (int i = ; i < res.size(); i++)
             cout << res[i].first << " " << res[i].second << endl;
     }
     else
     {
         puts("-1");
     }
     return ;
 }