CF615C Running Track

思路：

kmp + 二分。

实现：

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <vector>
using namespace std;
const int MAXN = 2105;
int neXt[MAXN];

void getNext(string s)
{
    int n = s.length();
    neXt[0] = -1;
    int k = -1, j = 0;
    while (j < n)
    {
        if (k == -1 || 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 = 0, j = 0;
    int m = s.length(), n = p.length();
    while (i < m && j < n)
    {
        if (j == -1 || s[i] == p[j]) i++, j++;
        else j = neXt[j];
    }
    if (j == n) return i - j;
    return -1;
}

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 = 0;
    while (start < n)
    {
        int l = 1, r = n - start, res = 0, pos = -1;
        bool flg = true;
        while (l <= r)
        {
            int mid = (l + r) >> 1;
            string tmp = y.substr(start, mid);
            getNext(tmp);
            int p = kmp(x, tmp);
            if (p != -1)
            {
                res = mid; pos = p; flg = true; l = mid + 1;
            }
            else if ((p = kmp(z, tmp)) != -1)
            {
                res = mid; pos = p; flg = false; l = mid + 1;
            }
            else r = mid - 1;
        }
        if (!res) return false;
        if (flg) ans.push_back(pair<int, int>(pos + 1, pos + res));
        else ans.push_back(pair<int, int>(m - pos, m - pos - res + 1));
        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 = 0; i < res.size(); i++)
            cout << res[i].first << " " << res[i].second << endl;
    }
    else
    {
        puts("-1");
    }
    return 0;
}